preventing screen resize on viao pcg-z505r?

I recently purchased an older sony viao for my wife as an internet and email machine, but she enjoys playing some of the nancy drew games. These games only play at a resolution of 640x480. When we first installed the game it ran fine at full screen. Recently, whenever she starts the game though, it resizes to a small 640x480 box in the middle of the 1024x768 screen, seeing as this laptop already has a very small lcd top begin with, it makes playing a point and click adventure rather difficult if not impossible. Computer is running win2k, can anyone tell me of a driver or bios setting that will make it run at full screen again? thanks in advance for any help.