For Reference....

I'm running 5 WoW's on one comp specs as follows. Only lag in Cap cities like Org or Shatt but its still very doable. My slave accounts are set to run at maxfps of 15 and my main is at maxfps 30. Cores are set at #1 for OS, #2 for main wow account, #3 for 2 slaves and #4 for 2 slaves.

MB-->PK5-E Asus
RAM--> 3 gig really cheap junk
CPU--> Q6600
HD--> SATA II 500 Gig
GFX--> 8800 GTS
OS--> Vista Premium