1) Are there any import scripts available? (threads and users (with passwords))
2) In terms of the URL's. We can take a look at the current naming with vbulletin but would need to know the target url pattern and then use ISAPI rewrite to perform 301 redirects.
Help with (1) would be good or we won't be able to move!
2. I suggest just doing a test installation... But you can change how the URL rewriting works if you want. But you'll need to recompile the code.