[kh99]

Well, I don't know of any way to do it with vbulletin. But if you imported your data into a table in the same database as vbulletin, then I'm pretty sure it could be done with sql. The membergroupid field in the user table is a comma separated list of ids, so it would take a bit of work there (I guess you'd need to add a comma or not depending on whether the user already has any additional member groups). Also if adding the group would affect the user's display group or ranks, then there's other updating that needs to be done to have everything consistent (if not, then I think just setting the field should be OK).