> Are there some NICs that work better than others?  I have 3Com
> 3c509b cards and have had no luck getting two of them working on
> the same system.  

These are some of the best ISA cards you can get. They will work, I promise.
:)
First though, do you have a PNP bios? If yes, set PNP-os installed to No. 

Second, head over to 3com's site and grab the driver disks for these cards.