I'm a huge fan of the Juniper/Netscreen 5GT series for applications like this. The type of port re-map that you mention in ScreenOS lingo is called "NAT-Dst with Port Mapping". There is *nothing* that you can't do with NAT on this box. It's got a great Web GUI, so it's easy to configure, but it's also extremely powerful and flexible. If you can't find a local reseller (you won't find them at Best Buy) then check eBay - you should be able to pick up a 5GT for probably $100-150 right now.
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