Clearly doesn't use avast, as there are many using avast with lessor resources than that.
I have 2GB of RAM on both my Desktop, XP Pro and Netbook, win7 starter edition (32bit) and RAM isn't an issue on either.
You only have to look at the task manager and you will see just how light it is. Then look at other resource hungry programs and you will see avast is a drop in the ocean. Examples on my system, Firefox, Thunderbird, MailWasher Pro, MbamService, Dropbox, my Desktop Calendar, they all may avast look positively anorexic on RAM use.