A nice little arrangement we've tried is as follows.
DSL router -> Freesco router (www.freesco.org?)
Freesco routers can run off a floppy and on an old machine with as littel a 8mb. We've found a p60 with 64Mb no disk and a floppy is perfectly fine for a small office setup.
With the router in place you're local network can now be hidden, leaving you spare IP addresses in your DMZ.
Freesco is quite funtional and thus its simple enough to map ports in firewall fashion to the local network...
I beleive freesco on one box will suport up to three network cards and two modems, so its quite possible to have multiple local networks or multiple IPs for the same service etc....
Definately worth a look as a really simple, low cost solution
Incidentally, from scratch it took us about an hour to set everything up.. So pretty straightforward
