My 2 machines are XP and Vista and what I ended up doing is adding another gateway route pointing to the CORE 192.168.80.1 interface, with a metric of 1 under Advanced Options of the TCP/IP configuration. So any default traffic goes to the default external router, and any internal traffice to the 192.168.80.x side. I can see my HPMediaVault now and map network drives to it. The only issue I have left which I can get around, is that the HPMediaVault uses netbios protocol by default, but netbios isn't routable I think. Anyway I just added the ip address of the NAS box to the c:\windows\system32\drivers\etc\hosts file.
-fins