Good ol' winsock and win95. We did something similar using a mere 2500 PCs with Novell shared storage over 40 IP subnets. IPX/IP was quite stable although we had to fudge the routers to get broadcast SPX packets across.
PC-NFS didn't scale too well and SunOS nfs was tempermental, never considered samba, however Novell file sharing was pretty good only to be let down by its self corrupting Networked Directory Services database.
I also vaguely recall you could create a static browser list in NT land as computers had a mysterious habit of dissappearing off the list.