Correct me if I'm wrong, but it sounds like you only have one monitor on your primary setup, and for PVP you wish to run all 3 accounts from your one computer?

Imho, having two monitors for your primary is the only way to go (quite frankly, whether you're multi-boxing or not, I consider this to be a great setup if you're a multitasker, and I can't imagine any multi-boxer that isn't a multitasker, that wouldn't make sense now would it?). It's a great investment all around, especially for multi-boxing.

However, there are some things to keep in mind when using two monitors that I've already dealt with on my own. If you are using XP, watch out for the dual-view bug which cuts your fps in half if. You'll want to use horizontal span, which fixes your fps issue, but quite frankly I hate horizontal span since everything likes to open up in the middle and get cut in half across my monitors. (If anyone else has two graphics cards like I did, this option won't be available!).

Vista however fixes this issue, so if you already are upgraded, or are keen on upgrading and have the RAM for it (2 gigs not enough for vista + multi-box imo) then I say give it a shot.