just get an ubuntu/knoppix livecd, and watch your "outdated" "underpowered" pentium 4 with 2G of memory come back to life.
i know this is offtopic completely, but what the hell is wrong with the world? i can understand planned obsolency is a viable business strategy but i would think there are limits before people get fed up and just turn and walk away without a word (the way vista has been received seems to point out that microsoft finally managed to go over that limit)
linux would give you the best of both worlds: a stable , reliable, easy to use and efficient OS, and making good use of your already very adequate hardware, i am unsure, however, how happy you would be without lightroom (no version for linux yet, i think, though there are alternatives), so this is unlikely to be a solution for you (though i am unsure: if you are willing to go through the trouble to replace your hw and migrate to another os, perhaps just migrating to a decent os without the hw part, and having the advantage you can use the same os on both laptop and desktop imediately, might make it worthwile considering -- it would save you a lot of headache in the long run; i have a hunch though you are not willing to let go of lightroom and the likes)
sorry to rant so far off the track, but something clicks up there when i hear people calmly talking about poor performance with desktop pentium 4's with 2G of RAM and so on, and how more memory and a quad core is required to get things done (not blaming the people for it, it just drives me mad)
in short, seeing as you are not very technically/it inclined (right?), maybe you can consider linux if you have a friend who knows it and can help you with the initial migration/occasional help, otherwise, probably not. you can still give it a try with a livecd though (nothing to install), just for kicks, to see how your computer is not really outdated, applications are not supposed to crash or freeze, and so on
ranting mode, off.