Right click on my computer, pick propterties. From there goto the advanced tab, click on the settings button under performance and at the bottom you have a setting for virtual memory.
The initial size is how big you want it to start at. The max is how big it can be automatically adjusted to if necessary. If adjusting it causing so many problems there's almost certainly something else wrong.
I don't know what else could be wrong but it certainly sounds like theres something else.. is your hard drive nearly full?