By the way streets, there is a link at the top of this page to the compatibility section of digidesign's website. (or you can just
click here )
On that page, if you select whichever digi hardware you are trying to run, it will tell you everything that you need to have to make it happen. the current lowest memory requirement is 384MB, but 512MB is HIGHLY recommended.
If you want to run samplers at the same time as/with ProTools, I recommend at least 1GB.