Linux

I think of Swap with some questions:
a)Will you run a lot of apps?
b)Will you run some apps for a BIG time?(server like time)
c)Will you run a lot of apps for a BIG time?

If any of this questions have a yes for answer, then you do need swap. But watchout, while it goes something like "virtual memory", having a lot of swap will only slow your system, and eat your space. The formula of swap needing space(swap=2*ram), works fine, but there's a limit, there is no point in having more then 1GB of swap space, since it will take forever to find the needed information in 1GB space. If you have an old system(like one with an HD of 5200 RPM), I would sugest not going past the 512MB os swap, and if you have an even older system(let's say a P133), I would sugest not using swap at all, or if you are gona use it, do not pass the mark of 128MB for swap.

And just to getting thigs right(correct me if I'm wrong):
The diference of Virtual memory, and swap partition, is that a swap partition is a predetermined space on the hd formated to do ONLY swap, while a Virtual memory will pick a part of the HD that you can use, formated with for exemple FAT32, FAT16, NTFS or whatever, and thus running much much more slower.