the pc's won't be on the same network because i have 2 isps. doesn't synergy require both computers to be on the same network?
OP why not put all 4 monitors on one PC and then use remote desktop to get into the other one. This is what I do for my internet boxes. I have two ISPs, one trading (100-mbit) and one internet/other (similar to FiOS). I use two routers, two workgroups, etc. and simply remote desktop into my internet boxes from my trading machines. Its easy and much better than screwing around with Synergy (though I am a big fan of Synergy). Send me a PM if you want more details on how my stuff is setup. Another plus is once you set up RDT you can remote into that box from anywhere. Cheers.