Camera Help

I had a Sony DSC-P51 Digital camera. I could resize the pictures to 640x480 dimensions on the camera itself. Well, my DSC-P51 broke, and now i have a DSC-P32. Everytime i resize the picture, it gives me the options of 3.1M, 2.0M, 1.2M, and VGA (Where it would normally say 640x480, 1280x960, and 1600x1200) I want my pictures to be 640x480 resolution, but come out do be 1600x1200 once uploaded on computer (Dont know what 3.1M, 2.0M, 1.2M and VGA Stand for). Any help would be good.

vga = 640 x 480

the others refer to how many megs the picture is

larger # = bigger pic