If I understand your question properly, you want to be able to find out which tables have FKs pointing to a PK. To do this, you need to look in the tables sysobjects and sysdepends (plus syscolumns for column names). The xtype in sysobjects lets you specify PK for primary keys. I hope that this helps.
Arthur Dent - "That would explain it. All my life I've had this strange feeling that there's something big and sinister going on in the world." Slartibartfast - "No. That's perfectly normal paranoia. Everybody in the universe gets that." Deja View - the feeling that you've seen this post before.