Help needed with Intel 8255x chipset

I was recently given a Japanese Toshiba Dynabook laptop which had WinMe on
it - I erased it and installed XP no problems, but I'm getting strange
behaviour from the built-in networking card (which is "Intel8255x-based Fast
Ethernet").

Basically every second it is sending 100 bytes of something (verified by
looking at the Connection status box) which is effectively jamming the
network. I have no idea what this is, and there are no unusuals processes
running. If I boot the computer without the cable connected and then
connect it when the machine has booted up, I do not get this problem ...
until another PC is turned on at which point the Toshiba starts jamming the
network again (preventing any computer from talking to any other).

I've never used a built-in network card or an Intel one - but I have setup 3
other PC's on this network with no problems.

Does anyone have any idea what might be causing this ??

R.




Anthony