No.
If you're using a version of vB where passwords are stored encrypted (hashed, with md5()
http://www.faqs.org/rfcs/rfc1321.html), which I assume you are, then no... because the hashing system isn't meant to be reversable.
You can try to brute force passwords.... but DAMN, you gotta have a fast computer.
I actually started writing one in C the other week, just for fun.... but upon benchmarking it, and finding that to go through all possible combinations, my 500Mhz AMD would take a few thousand years... I thought.... FORGET IT!!!