http://www.pcpro.co.uk/reviews/secur...tek-vigor-2955 - seems to be a fairly competent unit.
How CAN you forward a port to different IPs, how would it kow which one it was meant for.
To support a port forwarded service that may operate from different systems (but only one at a time), you need to use port triggering, where a certain condition that results from using the application (eg. outgoing on a known port), can be set to trigger forwarding of the required incoming port(s) while that condition is met