If you can use a static IP, just do that. On Debian systems this amounts to editing /etc/network/interfaces. Fedora/RH systems use /etc/sysconfig/network. The syntax is different.
If you want to continue to use DHCP on the interfaces, then you can "request" an IP for each from the DHCP server. To do this, modify /etc/dhcp3/dhclient.conf or equivalent to include yoru own lease configuration:
# .. your other options ...
Hope this is enough to get you going!