Here is what I did. I actually stored EQ in three different locations. #1 D:\EQ1, #2 E:\EQ2, and #3 E:\EQ3. The D partition is actually a SATA 10k rpm drive. I use that one for my main. Then I would run #2 and 3. I run a single MQ2 and it works fine though out all of them. If I ever needed a forth account up I would simply fire up #2 or #3 a second time.
By the way this was all with the following specs:
AMD 64 3000+ (2.01GHz)
3GB RAM
WinXP Pro (32bit)
GeForce 6800 (512MB) AGP!
I would also run MQ2WinXP and shutdown all of the erroneous services and explorer.exe.