Using Usergroup permissions in external files

I'm trying to create some pages for my moderators to use.

I know how to check to make sure the user is logged in. How do I then only grant access to a usergroup? Or a particular user? Or a couple of users?

[Admin]

if ($bbuserinfo['usergroupid'] == 2) {
  // blabla
}

Will only let users from usergroup 2.

[Sparkz]

And then I guess

PHP Code:

if ($bbuserinfo['userid'] == 2 || $bbuserinfo['userid'] == 3) {
  // blabla
} 

Or something, I guess