please see the reply here:
http://www.manhattangmat.com/forums/tha ... t5730.html
Also, please try to post questions only once, so we don't duplicate efforts!
Finally, in the other post, I forgot to address your question about the comma, but yes, that's generally true when you have "which" introducing a modifier. You can also have something like "in which" - in that case, you wouldn't have a comma before which.