What is the best way to improve my computer on a budget?

Honestly, there's not a lot you can do other than to replace your entire computer. You could upgrade the ram, as 1gb is way to low for any game that's came out in the last couple of years. But then you'd need a better CPU to even install it, and a better Video card to play it. That model of Dell doesn't really offer much in the form of expansions.