Playing around with a couple of NICs...
 

Ok, well i _think_ ive gotten two nics working under slacky, w00t :) but the only problem is, i dunno if thats for certain yet...

i loaded both the modules that they both use (8139too and ne2k-pci) and the 8139too NIC worked fine, could ping the network etc. Then i loaded the second module as well, switched the network cable over to the second NIC, and ran this command ifconfig eth1 192.168.0.210 broadcast 192.168.0.255 netmask 255.255.255.0
and when i do ifconfig, both NICs show up like normal, but when i try to ping the rest of the network thru the second NIC, theres no replies :(

Any idea's? maybe i didn't set them up correctly...

Im just thinking that the ping packets don't know which interface to go out and their still trying to go out eth0...

EDIT: after a bit of fiddling, ive found that when i go ifconfig eth0 down, then plug the cable into eth1 and go ifconfig eth1 up, eth1 pings the network fine, but then i cant go ifconfig eth0 up, and plug the cable back into it...im assuming i need to setup bridging?

If thats true, then what if i connected a laptop via crossover cable to this machine, and didn't want the laptop to see the rest of the network...can you filter bridging packets?

Hmmm, maybe im asking too much at once here, hehe

At a guess, I'd say you are using ip numbers within the same subnet on both cards...
This is a no-no for routing...
The pc, as you say, can't decide which one to send the packets down because both are valid...
Your default route would show one of the interfaces as default, and when you drop that NIC, the only card left that is valid magically starts to work...

The NICs need separate numbers and separate subnets to work together...
Have a look at this Networking HOWTO