The drivers will be part of the distribution. Hopefully RH will just auto-magically find them as it is prone to do, especially with 3com as they're public with their card specs and therefore loved by the Linux community.
As to which card? I should poke over to
www.google.com/linux and see what the kernel modules are for either of those cards, but I'm 2 minutes short of lunch. Honestly, if you have the space in the crate, just slap em both in and see which one is easier. Getting networking running under Linux these days is a joke, with the only remaining issue being good old legacy ISA gear.
If after installation the card(s) aren't found by RH, its just going to be a matter of modprobe'ing the drivers with the IRQ or IO setting as an argument.
Cheers,
Finegan