I saw a few poeple that had this problem, but wanted to share my non-reinstall solution.

After upgrading to Windows2000, I had no TCP/IP function via network adapter, or dialup with a modem. Furthermore, I would experience a 720 PPP error when attempting to authenticate with DUN to my ISP.

After removing TCP/IP from the network properties of my LAN and dialup connections, I noticed that TCP/IP was not listed as a protocol that I could add.

Removing and reinstalling Windows2000 service packs did nothing.

What I did do is copy the C:\WINNT\SYSTEM32\DRIVERS\tcpip.sys and C:\WINNT\INF\nettcpip.inf from another Windows2000 PC onto my problem PC. Then you can browse for a protocol that isn't in Miicrosoft's list, and point to the C:\WINNT\INF folder. TCP/IP will be selectable after this. The network properties should update and rebind properly.

best wishes to anyone that killed an entire day on a MS Win2K upgrade like I did.