I was following up on something today and came across an article that may help you here... When you get a chance, look at this:
http://social.msdn.microsoft.com/Forums/sharepoint/en-US/c32bc150-7249-423d-8018-d2f23afc1f3b/getpermissioncollection-converting-permission-mask-to-roles
http://social.msdn.microsoft.com/Forums/sharepoint/en-US/c32bc150-7249-423d-8018-d2f23afc1f3b/getpermissioncollection-converting-permission-mask-to-roles