Windows 7: How to isolate a Win 7 64x from other PCs in the home?

Hey there -- Cool site! Could really use some help -- tons of googling and just confusion. In my home I have a laptop (Linux) and 2 desktops (one dual boot Linux/Win 7 home prem 64x and one Windows 7 Pro 64x). The latter is used for a small startup business with very strict policies -- only a few needed IP addresses allowed. I'd like to isolate this from the other 2 in case they are compromised. Question is: Can I "dual NAT" and use the LAN side router (connected to the Windows 7 Pro) to completely isolate this machine from the others (maybe implementing a 10.0.0.x network designation as GRC outlines), or will this not properly defend against network intrusion (which has happened) or rootkits? Alternatively I've run across brief talk of using 3 routers to establish 2 completely segregated gateways but cannot find any explanation how to do this. My budget is tight (or I'd get a separate line), so I'd rather just get the routers. Any ideas/alternate suggestions or references as to how this can best be done? Thanks much!