You can never have too much RAM. Now sure, they say that more ram will give u slightly slower sandra marks, but not even close enough to notice in everyday use.
With 64bit cpu's coming into the mainstream, having more than 4GB no longer presents the problem it used to.
If I had it my way, I would have an enormous amount of ram and run ramdrives. I run ramdrives sometimes for the heck of it, and it is unbeilievable how fast you can transfer 100MB+ files in explorer.
If you have the money, 1GB is recomended, unless your doing rendering or running a server, then more would help a lot. If not, then dont get any more than 1GB unless you really have no budget at all.