One network card with 2 IP adresses

Every ethernet interface can have any number of aliases in the form

ethX:Y

For example, since you have one ethernet card, it's probably "eth0". You
can have as many IP's as you want that attach to the "virtual ethernet
cards" eth0:0, eth0:1, eth0:2, eth0:3 . . . you get the idea. To assign an
IP to one of these cards, just type (as root)

ifconfig eth0:1 10.1.1.2 (or some such address.)
That's all there is to it! If you want to make these settings permanent
over boot, add the 'ifconfig' line to /etc/rc.d/rc.local or put it into
the redhat network startup scripts.