If anyone's using Path Finder[1], I wrote a quick modification of the "Open in TextMate" applescript that works with it[2]. It allows for selection of an individual file, or creation of projects with multiple files/directories selected.
Cheers, Brett
[1]http://www.cocoatech.com/ [2]http://blog.circlesixdesign.com/2007/01/18/textmate-in-pathfinder/