sata2 drives have a jumper for backward compatbility so it should work fine , but it seems some of em have issues with nforce4 have a look at this thread
http://forums.nvidia.com/index.php?showtopic=10755&st=0 , so get it and hope youll get a good one or just take a samsung with 3yr warranty , hds are cheap i suggest youll do yourself a favor and get a bigger one for bit more , and keep that 40gb dont take it out it will be very useful for backup and plain storage