Adding more RAM is always a cheap way of speeding up your PC because, simply, more ram means that less virtual memory will be used and as chip memory is faster and has faster access times than a harddisk has the overall PC speed increases.
Nonsense.
If you have 2Gb physical RAM and you are using 1Gb total memory then buy more RAM won't make it go any faster, because you are already never using the disk for swapping.