This goes to show my inexperience, but I don't have subversion installed so I can't run the command. How do install it?
Perhaps Martin Ott's package might work nicely for you: http://www.codingmonkeys.de/mbo/articles/2006/11/08/subversion-1-4-2
If you use fink or DarwinPorts, you can install it from there as well.
Additionally, is there any info in the wiki or elsewhere about how to use the terminal from TM?
There was talk of some plugin called TerminalMate (I think)
I never installed it, but perhaps you can search the list archives for it -- it maybe what you're after.
-steve