While 3Com makes excellent cards, many times you won't find drivers for WinNT or Win2000. I'm not talking about other OSes, such as Linux, BeOS or Novell or even anything else what will come out in a near future.
Intel on the other hand has drivers for everything, WinNT and Win200 detects my Intel 100+/Management Pro without even asking for drivers. This network card works flawlessly in RedHat as well.
As far as performance of the network cards, trust me,
they all are identical 