can iSeries handle nat for small pc network

Have a customer at v5r2 on small model 800 with single ethernet card.
Changing isp, and new isp (Bellsouth) will not do nat or dhcp - they only 
deliver 
a preprogrammed firewall (we can't touch) with public address. (For 
over $260 mth they offered to manage "something" to do this). Current isp 
had too many outages.
There is no pc "server", only pc workstations, and a windows solution
is not an option.
I know iSeries can do dhcp, but can it (or should it) handle nat for a 
20 pc lan? They are all 10.x.x.x (iSeries has both 10.x.x.x and public,
and is doing light web serving). PC users do a fair amount of web surfing 
for work. Or should I have them purchase a router to put inside the firewall to 
do nat
(and what's recommended that will not ever have to be reset-will be on ups)?
Shop has no onsite tech, and management wants absolute reliability and uptime 
24x7x365. 
iSeries only comes down for monthly ipl at 3am (not really needed) and cume 
ptfs.
jim