Actually it really depends which backport you have or if you even have a backport at all.
Older Version: C:\Documents and Settings\<my username>\Local Settings\Application Data\Tremulous
New Version: C:\Documents and Settings\<my username>\Application Data\Tremulous
No Backport: NO DIRECTORY!
If you do not have a backport, please visit
http://trem.tjw.org/backport/Select win32, download the .exe and then replace in: C:\Program Files\Tremulous
And overwrite your existing tremulous.exe
Run the executable and then look in directory: C:\Documents and Settings\<my username>\Application Data\Tremulous