First, the maps should go in the ~/.tremulous/base folder, of if not, it should let you run it as some other user account.
Lots of servers will have a trem account, and some not root access.
You can use test -w to check if you can write there.
Also, tremulous.info has before asked people not to take maps from there with scripts.
Also, remembering the folder isn't necessary, as unless you run it with . ./tremmaps, the change will not be remembered. (I used to make the same mistake).
Sorry my last post was so critical.