By default, windows sets this up for you. You can mess with it by right clicking on My Computer, Proporties, Advanced, Settings by Performace, Advanced, And Change by Virtual Memory.
What I usally do is input a range that's about 1.5 times the amount of memory you have. Say you have 256M, I enter 512M to 512M. BUT, your machine works fine as it is. And you don't want too much as it obviously takes away from your HD and you degrade your performace(HDs are MUCH MUCH slower than RAM)