This is actually not a bad Idea. If you have a little extra money I would look at a new computer. You can get 4 times the computer these days for a couple hundred dollars. But if you don't have an extra couple hundred buck RAM is your best bet. although the RAM will cost more now then it did back in the day, as it is harder and harder to get RAM that old.
+1 on NOD32, its written in assembly code so it takes up 25% of the system resources that the Bloatware programs like Symantec/Norton or McAfee do.