I would check the wiki aswell there is plenty of stuff there. Aswell through all the threads on here. But this is what I would sugjest you looking at first before anything (hardware specs needed for the min of running 5 accounts)

http://www.dual-boxing.com/wiki/inde..._can_handle_it

In short from what I have read (since I have been researching before I build a rig to 5 box)

Need a quad core processer (a 2.6 is able to run 8 copys of wow)

You will need atleast another gig of ram.

Not sure if you will need to pick up better psu but possibily.

Aswell as you will need 2 hds that are running at 7200rpm

(Mind you this is just what I have researched through the site and with that I would sugjest that you look further into the site, there are tons of posts, the wiki has allot of info aswell)