|Then go to perfmon maybe, look for cpu and memory issues.|
This is still an odd way to do stuff. On many OS's ping to localhost will work with no nic installed. Only suggested that tcp/ip stack is working. Not sure if MS changed that in xp.
Kind of got me contused here. You say two nics do the same thing. That kind or rules out either nic and drivers too.
Ping is a low priority so maybe other tasks are at work. Guess you could also view wireshark for more info on lan traffic.
Could ring the ethernet cable maybe crosstalk or other fails on a bend or connector.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10