If I were you I'd go for 512 of some nice DDR. 256 will get you by in XP, but 512 is the sweet spot for the OS and most users who game and such. XP will page a LOT less to your hard drive in games with 512 megs, and you'll be bale to multitask a bit better if you run any memory intensive apps, as stated above. If you're gonna be doing some overclocking, get some nice PC2700 or PC3000 and you'll close the gap between DDR and RDRAM by a bit.