It wasn't too clear above, but the more system memory you have, the less virtual memory you need. On greater than 128 but less than 512 (384 or 256), you can probably get away with 200 or 300MB for virtual memory. Above, it was stated as the same amount as your system memory, which is a pretty good guideline, however with 512 or even 384 you shouldn't need more than 100 or 200MB, and with 192 or 256, you'd need at least 300 or more for 192. The reason the min and max values should be set to the same size, is so windows doesn't have to adjust the size of the pagefile constantly, and use resources to do so.
My own personal formula is to shoot for a total of 644MB for system memory + pagefile size.