Vanilla 1 is no longer supported or maintained. If you need a copy, you can get it here
Impossible or not? I'm not good at converting databases as I usually end up failing every time.
But, I want to know how hard it would be. I just want basically the user table converted. I don't care that much about the posts or stats.
After I post this I'm going to look at the SQL to see how similar the database layout is if at all similar.