MEMORY
Consider memory needs
Biggest memory difference between systems is bit-depth on the monitor(s). If you're running in 640x480, 256-color mode (8 bit), and he's running in "millions" (24 bit) at the same resolution, that's 2 bytes per pixel
difference. At 640x480, that's 614,400 bytes - almost enough to account for the 1Mb difference you're seeing. If you're both at 832x640, the difference is 1,064,960 bytes. If he has a bigger monitor than you (and your windows are accordingly bigger on his Mac) in addition, it can _easily_ take a couple Mb more. Plus offscreen gWorlds count as well!
Moral: Always either allow enough memory "room" for your program to run in "millions" of colors, or always specify the bit-depth of your gWorlds, or "force" the user's Mac to a specific bit-depth.
Bill