Log on to Domain over PIX Firewall

I am currently figurin gout why Win9x clients(private network)cannot log on to a Win2K PDC(outside network) over a firewall? For trial purposes, i hav opened all tcp as well as udp ports so that nothing gets blocked. Also i noticed WinXP and Win2K clients can get log on just by pointing the DNS to the Win2K server for resolution. What did i miss out?