|For starters, you need to understand what the pagefile aka swap file aka virtual memory is used for & why:|
When your system runs low on RAM because an application like Firefox is taking too much memory, Windows moves the least used "pages" of memory out to a hidden file named pagefile.sys in the root of one of your drives to free up more RAM for the applications you are actually using. What this actually means to you is that if you've had an application minimized for a while, and you are heavily using other applications, Windows is going to move some of the memory from the minimized application to the pagefile since it's not being accessed recently. This can often cause restoring that application to take a little longer, and your hard drive may grind for a bit.
NOTE: In Win9x systems it's named Win386.swp, but in newer systems (Win2k & up) it's named pagefile.sys.
Remember that virtual memory is extremely slow compared to RAM. There is no substitute for physical memory. No amount of tweaking of the virtual memory settings can make up for a lack of RAM. And there is a LOT of bad advice out there on how to configure the virtual settings. Generally, the best thing to do would be install as much RAM as possible (depending on the OS) & just let Windows handle the virtual memory. The only "tweak" that will increase virtual memory performance would be to put it on it's own partition on a separate hard drive.
BTW, don't confuse virtual memory & virtual machine, they are 2 completely different things.