1. Click "My Computer"
2. Click "Local Disk (C: )"
3. Click "Program Files"
4. Look for "Tremulous"
5. Once yo have found, click it
6. Now look for you "base" folder
7. Now there should be a file that says "Screenshots"
8. Click again on that folder, and there you have your screenshots.
9. Once you taken a certain amount of screenshots a Base 2, Base 3, etc, will appear, and in the screenshot folder, thats where it will be.
And using the computer URL bar is really a useless way to find things, it is said it works better on Vista, I have yet to try it out.