Interested in multi-instancing and I have a few questions

I'd recommend looking at both the hardware and software options available.
I personally went with Keyclone as the software option.
That might or might not be the best option for you. Everyone is different, and has different perceptions.

I'm running 5 copies of WoW smoothly. My system was near top of the line a year ago, so is still decent today.
WoW runs well, but most of my options are turned down; one account with every option up is a little smoother, but five is definitely playable.
Vista 64-bit, Q6600 o/c to 3ghz, 8gb DDR2 pc3200, 8800 GTX 512mb.

Over the summer I've upgraded from a 22" Samsung 225 BW to a 30.5" Samsung 305 T.
I much prefer the real estate on the newer monitor but if I can make room on my desk might run both monitors.

I'm thinking of upgrading my video card to a Sapphire HD 4870 X2, I'd like to have graphic options cranked for WotLK and still play smoothly.
I know that's overkill for WoW, but its barely in the budget, and I'd really like to have the graphics all the way up.

Thanks for all the information guys. I didn't realize that Keyclone did so many other functions in addition to just passing keystrokes. I'll be sure to get a copy of this. I think I'm going to set up <that which must not be named> http://solidice.com/images/Ninjafade.gif

I could do a 30" screen, but I'm pretty anal about my multiple screens being the same size.. I suppose that doesn't leave 2 30" screens out of the picture :). Come to think of it, a few guys dual boxing on a private server could easy fill out a 40 man raid.. interesting.