If you're on XP, then 1GB will usually be ample for most people. By most people I mean folks who do a bit of emailing, surfing, downloading, digicam and ipod connectivity etc
Vista will need a minimum of 2Gb, even if you just want to do some adding up using windows calc
If you are into heavy aplication, like advanced photoshopping, video or music editing etc, then as much as you can get, but be aware that XP can only see 3.3GB or thereabouts.
If you are into heavy aplication, like advanced photoshopping, video or music editing etc, then as much as you can get, but be aware that XP can only see 3.3GB or thereabouts.