BF1942 is a BIG memory hog. Even with 512mb of ram, it'll easily use up to 75% of it. Add on top of that the bloated nature of Windoze, and 256mb will feel like 64mb.
But the virtual memory issue may be becuase your running out of space for the swap file. You'll either have to delete some stuff from your harddrive to give the swap file more space, and/or increase the swap file size.