model #, please. off the tag on the back. or maybe embossed on the front, too. for example, my HP Slimeline is an s3100n. Just for an FYI, OS isn't important for this type of discussion. Whole issue is how much physical RAM can you're machine be upgraded to regardless of your OS. Although, for your purposed, XP is better than Vista, since as you probably know, it takes signficantly less RAM too run. Which means that more games are available to you. What I was saying before, if your computer has even less RAM than the game calls for, your chances aren't good regardless of what OS or any other hardware you run.
Re-Edit: Sorry, Terri, I didn't read your post about game booster. Then I wrote and explanation here thinking that said 120 instead of 1280. Sheesh! Off to the optometrist. Still, I leave the gist of it, since your wondering about RAM in general. But I would SHOCKED if a machine with 320 can run a game asking for 1280. Maybe I'm way behind on the curve for games - like I said, developers exaggerate - but, are you regularly able to run games with specs WAY above what your computer has?
It breaks down like this: Windows says XP needs a BARE minimum 64MB of RAM. But that's nonsense.re With 64, XP can load but practically not do anything. The recommended is 128. Many say you need about twice that, 256, to run smoothly. If you look at it that way, you can see that your getting pretty close to the 300 plus you've got and there might not be enough left some games. However, customizing your system to run more lean and mean or using an optimizer like Game Booster can get you down away from that 256 and free up more to run larger games. One way is to make sure you don't have too many things loading at startup that you don't need. One way to tell is too look at your system notification tray. All those little icons next to the clock. If you've got half a dozen or so, then you're running OK, although not everything shows up there. I've seen people have 30, which is crap, crap, and more crap. Turning that stuff off will lower your RAM usage.
To see most, if not everything, you can type msconfig into your Start>Search box (or your Start>Run box if your using the Classic menu) then double click or hit OK (depending on which menu). MSConfig configures your booting options, though it's really for troubleshooting rather than controlling that stuff. It has a tab that lets you see mostly all of what is booting on startup, and if you don't recognize something, google it. Anything you don't want running all the time, has to go. We can suggest various utilities for that - some you may already have - because, if you use MSConfig, you'll get an annoying message every time you boot up that you're blocking stuff, because that isn't really what Config is for.
Also, some say that the various Service Packs, like SP2, use a little more RAM, which is likely, but I haven't been able to come up with an exact spec for you, yet. But the numbers above are in the ballpark.