PC Freezes when conncted to LAN/internet

this is my hardware setup: intel celeron 800MHz CPU. ASUS cuple VM board. Generic 56K modem.
Realtek NIC.

Everytime i connect my workstation to the local area network, it freezes after a few moments. The same is true is i dial up to the internet. The same results also if i install VM ware. I tried swapping the modem and/or NIC to different expansion slots but its still the same. My applications are working fine. What could be the possible problem here? anyone???? thanks in advance