yes .. if you are a lisenced vbulltin member download impex.. this tool can be used to convert several databases to vbulletin.. GOOD LUCK....
The key to this is to make a backup of your live SMF DB and use impex from the backup DB. I've never seen anything go wrong with impex on the donor DB, but its good to be safe .
You can, but don't you need your members to reset their passwords after the conversions? I find this very annoying if that's the case.
The passwords will have to be reset. Impex does not import passwords at all. You will also have to remove certain usergroups because SMF's user groups are different and they will be duplicated in VB and you will have to give the proper permissions.