Parts of system code and device drivers can be swapped out to paging file when the system needs more RAM. The system slows down when it needs that code or drivers since it must load them from the paging file. Windows stops while the required code is swapped in or out of RAM dependent on very long hard drive access times. If you have more than sufficient RAM, disabling Executive paging should improve performance.
I now have 1GB RAM but I had no problems even with 512MB.