If you have two IPs, you can set up two instances of AOLserver for
each site and have their main and subquery pools point at the same
datasource. The two AOLserver instances will each have their own db
pool, that is, but share database tables because you'll be using the
same datasource to open handles in those two separate pools.
Then one AOLserver/ACS instance only has user registration and
bboards, your other installation has whatever else you plan to run.
As far as hosting more than one IP on a single network interface, if
you're running RH Linux check out the script
/etc/sysconfig/network-scripts/ifup-aliases. It's very easy to use
and lets you set up ranges of IPs that each network interface on your
system will service.
