Don, I'm glad you've had lots of success with your 3COM cards
For a brief while, I had a borrowed 3COM ISA card that worked just fine on Red Hat 5.2 (fall 1998), so I have known for a long time that just because a NIC is an moldy old ISA card doesn't mean it can't function. I have no grudge against your cards or any others in the 3COM product line.
My point is that if you have an old card lying around, it's best to check to see if it's listed on the Hardware Compability List(s) before trying to configuring it. The lists also offer suggestions for alternate drivers (e.g., 3COM's own drivers for the 3C905C models) as well as "community-offered" tips on configuration and compatibility so if one is having problems with hardware configuration, it might have been easily solved by reading the notes first.
