I wouldnt use anything less than 512 myself... I run win XP and it uses 180 by its self, that leaves 75Mb for apps and games hmmm not enough I think.
So the simple answer would be stick 512 in and every thing should run hunky unless you do heavy duty video or 3d editing
512 is a necessity almost. 1024 is best. I suggest getting a 512 stick. and in the future, get another one. Get a good brand. and try to get ones that have heat sinks. Once you hit 512, heating becomes serious.
Yeah, use at least 512MB. If you have an ASUS mobo equipped with a dual channel memory controller, use two sticks of the same brand 256MB to take advantage of ASUS' Twin Bank technology for doubling memory bandwidth.
if you have a tight budget than i would get 256MB memory. if you find it is unbearable just get another 256MB stick and add it to your computer to bring total to 512MB. when i used 256MB it wasn't running much slower. not noticeable anyways