Internet sharing on LAN

Current LAN:
Win2000 Advanced Server (1)
6 nodes (8 having win98,1 having win2k professional)
win2K Professional machine has 2 NIC’s.
1 – for Local LAN
2 – Cable Internet

I wish to share this Internet connection on the Local LAN.
I also need a good diagnostic utility to check the network performance & troubleshoot problems like file sharing access denial etc.

Viplav