How do I allocate more video memory in Windows XP?
If you have a motherboard with built-in graphics card, you allocate the video memory from the BIOS setup program; the maximum amount of memory you can allocate depends on how much RAM you have installed. So, if you can’t increase the amount of shared memory in BIOS setup any more and you still want to have more video memory, just upgrade your RAM and increase the shared memory (in the BIOS setup program; you can’t do that in Windows). If you have a separate video board, that board has a certain amount of RAM and it cannot be increased.