I’m still trying to get rdebug to debug my script/server on a remote machine from Textmate and still no luck. However, I had another play with rdebug and have finally managed to get the client-server mode working. I never managed to find any blog posts that worked for me, so hopefully this will work for you!
On the server (from your Rails application root directory)
rdebug -sw ./script/server
On your local machine
rdebug -c -hIP.ADDRESS.OF.SERVER
Just as a reference I’m running ruby-debug 0.10.1 as a gem on OS X 10.5.4.