might I ask why you don't want to install more RAM?
the 5150 board can take 4Gb in all across 4 DIMM slots. a 4Gb kit will only cost you around £60, 2Gb kit for around £30 that, depending on your current config, you can add to 2Gb of your existing RAM or an extra 1Gb for £20. if you're already committed to buying the OS at around £70, I would suggest it's worth putting another few pounds that you might spend on a take-away in one night to better the performance of an aging machine.
don't get me wrong, I'm not saying you should or you must, just that it's recommended. this is just to give you a idea that it's actually not expensive to make a noticeable difference.
