I was one of the people having problems with Mail 2.0 in Tiger... it would constantly crash. I read of people fixing the problem by removing plug-ins such as the HTTP plug-in, but I hadn't installed that or any other one to my knowledge.
Then I remembered that I had installed PGP, which adds a plug-in to Mail (and Entourage). After removing PGPmail.mailbundle, Mail has worked like a champ.
For anyone having problems with Mail, check this folder:
~/Library/Mail/Bundles
and remove anything in there (just copy it to the desktop to test).