One other thing I'd look at would be how / where linux places the new NIC's... Your first pair would likely have been detected and placed on eth0 and eth1. IF Linux detected and loaded drivers for the new cards, even though the first 2 have been removed, they would probably be placed on eth2 and eth3. Of course, unless you've already changed this, LMCE is configured still to use eth0 and eth1, so your network can't work. If you've not already changed this setting, go to console, do "ifconfig", find out if the cards are detected and usable, find out which 'eth' each is seen as, and change the networking settings in LMCE to reference them appropriately.
Just my own thoughts... I've experienced this very issue (NOT with LMCE, but with Linux in general), and wrestled with it for hours... Hope I'm able to save you some time...