Is this specification able to run 5 instances without problems?

CPU: P4 2.4 Ghz quad processor

RAM: 2Gb DDR3 (Possible to upgrade to 4Gb, should I?)

Video: Enforce 8800 Ultra 768Mb

S-ata 150 HD

I run on vista, never had a compatibility problem since I started with it and love it so far really. *shrug*

I'm considering going 3 accounts, and maybe even 5...