So you want to put a webcam farther than the normal cables you can buy, huh?

Here is what I did, and its working (see the cam working on www.k5ktf.com ? ):

What we will do here is parallel the pairs to alleviate voltage drop across the CAT5, but also using the twists properly to avoid noise and interference.

LEGAL-EAGLE NOTICE:
Whatever you do with the following information is SOLELY at your own risk. If you do something stupid, dont try and shift the blame to someone else. Your doing it, its your responsibility. Im just telling you what I did. If I jump off a bridge, you gonna follow then sue me??? lol
Also, I did this using my own wits. I did not read this on any web page or hear it from someone. Im smart enough to think for myself, thank you :-)

List of things to gather up:
CAT5 cable, about a foot longer than what you need for the USB extension
Heatshrink tubing in 2 sizes, one big enough to fit over the diameter of the CAT5 cable, and one small enough for the indiviual CAT5 conductors.(or electrical tape)
Ohmmeter/DVM
1 USB extension cable, with a USB A Male on one end, and a USB A female on the other. (you should be able to plug one end into the other, if not, you dont have A-male to A-female)
Small soldering iron (30-40 watts should be fine) and 60/40 (63/37 for those who have it) rosin core solder
Heat gun/Cigarrette lighter/source of heat (to shrink the heatshrink tubing)
Wire strippers/diagonal cutters/etc
Vinyl Electrical tape (any color except fuscia)

1: Take X number of feet of Category5e (CAT6 or better should work better).
2: Purchase a USB A-male to A-female extension cable. Length does not matter, you need the male and female ends.....
3: Cut and slip heatshrink on both ends of the CAT5 that is large enough to cover the full diameter of the CAT5 cabling plus a small extra.
4: Strip back about 2 to 3 inches of the CAT5 outer covering insulation. DO NOT nick the individual conductors' insulation! (if needed, strip off some and use the pull-string in the cable to rip(cut) back more then cut off the excess covering)
5: Untwist the ends of each pair ONLY as much as you need to be able to solder and insulate properly. The less the better!
6: Cut the purchased cable about 4-6 inches from each connector. You want enough that you can work with, taking into account if you make a mistake you might have to cut back more (leave a couple mistakes length :-) )
7: Strip off the outer insulation from the USB cable, again, DO NOT nick the individual wires' insulation. (using diagonal cutters, you can cut nips from the end in to avoid cutting the wires)
8: Meter-out (tone, whatever) to figure out which color wire is which connection inside the USB connector. It does not matter left or right, pin 1 through 4. All we need to know is which 2 are the outside pins, and the 2 inside pins (outside being +5 and GND, the inside being USB + and - ).
9: On the CAT5 (or equivalent), separate the orange and green pairs. These will be the USB data signals, since the orange and green have more twists usually, so should have better signal integrity.
10: Pair the 2 "colors" from the orange and green together (strip off 1/8" - 1/4" or so and twist the conductors together), and the 2 whites. So by now, you should have 2 "conductors", the colors and the whites (Not referring to racial equality here... :-) ).
11: Do the same with the Blue and Brown pairs, matching up the colors and whites.
12: Slip on heatshrink tubing of appropriate size for the individual conductors (or just tape later if your sloppy) and tie the Orange/Green colors to the wires corresponding to one of the center 2 USB connector pins, twist, solder and heat the tubing (or tape).
13: Heatshrink and tie the whites to the other of the center 2 pins.
14: Do the same with the Blue/brown pairs, but tie them to the outside pins (dont forget your heatshrink.....).
Make sure that you do the EXACT same on both ends of the CAT5 with the USB connectors.
15: Use an ohmmeter to make perfectly sure that pin 1 matches pin1 on both ends, pin2, etc. This will also verify you have made good solid joints and soldering.
We are looking for straight through connections between the USB connectors.
16: Once you are sure you have all 8 connections correct, toned out to have pin1 match pin1, etc, then slip the heatshrink over the entire assembly and heat until it shrinks and seals the splice.
17: Now you can attach your webcam to the female connector.
What I did was using electrical tape, I wrapped 3 turns below the connectors, then VERY TIGHTLY went up across to the backside of the opposing connector, then 2 turns around behind that connector and back down across.
This was meant to keep the USB connectors (from cam and the extension) from slipping loose. I did this wrap 4 or 5 times, to have good tension to keep the 2 connectors together.
Once I was happy that they wouldnt slip loose, I neatly wrapped the entire thing 2 times for weatherproofing.
18: You can TRY plugging the USB male end into a USB port on your computer, but dont expect much luck! It is better if you plug the extension in to a powered USB Hub (2 ports or more), as this seems to correct any timing issues that the PC port just wont do.
If you plug into the PC directly, expect the FOUND NEW HARDWARE, but that it may not figure out what the device actually is. That is the symptom I had.
When I plugged it into the hub after, then the FOUND NEW HARDWARE was followed with CREATIVE WEB CAM and then any webcam software (Yahoo, YAWCAM, etc) could use it without a problem (see the main K5KTF web page).

If you plan on putting your camera outside/up on a mast/on an antenna/etc, you may want to carefully look at the camera itself and consider what would need to be done to weatherproof it (I write this as Hurricane Ike is about to drown Galveston, and hopefully send rain our way up to Austin tomorrow).
On my webcam, there was a groove all the way around where the 2 halves of the plastic come together, and where the hardwired cable exits the body.
If you do this for weatherproofing, DO NOT stretch the vinyl tape!! Over time, the tension will eventually pull itself loose.
Just pull the tape off the roll, cut it, and just lay it on the surface, then press firmly, but again, do NOT stretch it.
I just used standard vinyl electrical tape all the way around that groove, and with a small piece over the top of the cable strain relief, to keep any rain from entering the body.
Also, the way this camera is, it had a hole in the bottom for the mount. The way I mounted mine on a PVC endcap, I left a hole that would let any water or condensation that may build up to drain out and not cause water to fill the cam (better known as a weep hole).
We have had at least 3 or 4 good downpours/thunderstorms since mine went up, and at night I can still see the little green LED seemingly floating up in space :-)

Hopefully you have as much success as I had.
I made the first one (the one currently running that cam) about 30 feet long.
Once the tower and mast go up, Ill need about double that, so I may be experimenting here soon on exactly how long I can make one without ill effects.

If you have any questions, ideas, suggestions, better information, or to share stories about one you built, etc, Id be glad to hear it!
Just email "Jim at mycallsign.com" (replace mycallsign with what my call sign really is :-) )

73's and good luck!