sounds like your drivers are rather well balled up
you can try to uninstall the ethernet driver you have and then install the correct one
worse case senario ........ perform a win xp repair install ........ this will only remove all drivers from the windows system and allow you to start driver install from scratch ....... always do the chipset first ! then the others
http://www.michaelstevenstech.com/XP...install.htm#RI
this wont mess with your programs or data
it will perform another sequence that looks like brand new windows install ..... but its not ....... its just a brand new hardware detection and set-up