Granting Login to specific page only if member belongs to a certain usergroup

I've coded the part where users can log into a seperate page using their vB login information, but how would I get it to only allow users of a specific usergroup?

Better yet, I have the contributor hack installed, is there a way to detect if a user has a contributor status, and grant them access, denying others?

Thanks,
Alex

[DirectPixel]

I think I've waited enough minutes to bump this thread.

[Xenon]

PHP Code:

if(in_array($bbuserinfo['usergroupid'], array(5,6,7,x))) 

where x is contributor usergroupid