The question is about the desktop, right?
You have a gig of Ram and probably a large hard drive. I doubt you will gain anything from increasing virual memory.
Before hard drives got huge it was an OK idea. Only a small part of the hard drive was used for virtual memory. You could raise that amount and see a performance gain. Now, hard drives are magnitudes larger and they have plenty of virtual memory space.
Basically, when the computer is doing some serious number crunching, you will see the hard drive working. That is virtual memory - space on the hard drive is used to store information temporarily. Naturually if you are opening and closing programs and files, the hard drive activity is just reading and writing the normal stored information. These days there is little reason to adjust for more virtual memory.
** IF you dont' have enough RAM you will experience "hard drive thrashing" no matter how much virtual memory is set aside. IF a person experiences this they should just buy more RAM.
IF you want to experiment with virtual memory:
Right click on My Computer > Properties > Advanced Tab > Performance Settings button > Advanced Tab and then virtual memory is at the bottom.