Nevermind... I thought you wanted to select the pool based on the source IP address. Can you elaborate on what you're trying to implement?
Do you have two virtual server IP addresses which you want to map to two server IP addresses? If so, you could create one VS on 1.0.0.1 which points to a pool containing 2.0.0.1 as priority 100 and 2.0.0.2 as priority 1. And you can create a second VS on 1.0.0.2 which points to a pool containing 2.0.0.2 as priority 100 and 2.0.0.1 as priority 1. The higher priority pool member would take precedence as long as it is marked up. If it marked down, connections would go to the lower priority member.
Or have I misunderstood your scenario?
Aaron