Heres an interestiong one thats got me flummoxed...
Dell Inspiron 2650 laptops work fine on peer to peer workgroup. Install SP2 and they report "cable unplugged"
Update to latest 3com network drivers (2003!) still same problem. Link directly via a crosover cable to a none SP2 machine, hey presto the two computers see each other!
Have tested network cable (fine) have tested swithch (fine) ipconfig says "Media state......:Media disconnected"
Firewall (Zone alarm) disabled, uninstalled, you name it, no difference. Windows Firewall off too.