I have an older computer, too. It's a P4 running at 1.6GHz with XP. I upgraded to 1 Gig of RAM from the, I think, 256M that it had. I noticed a huge difference. Of course, it matters how many applications you are running at the same time. If you have a trading platform, charts, IM, webpages, and more open at the same time then having more RAM will definitely help. I run quite a few applications at the same time, so I would still notice a bit of a lag when opening new programs. It's a pain when you just want to open your music player or check your email while trading. I then added one more gig and went to 2 gigs of DDR RAM. Two gigs is pretty good. RAM is the cheapest and best upgrade you can do. I'd say get as much as you are willing to pay for.