Onboard video card memory access

Hey,
I have an old mother board (Intel i845 GLLY) with onboard video card. I am using the onboard video card only as there's no AGP slot and am not very rich:-) Anyways, can you please tell me how to use the onboard video card's memory to write into it?

Under windows - you cant because of protection measures..you can use a graphics lib like OpenGL or DirectX

In DOS, look up mode 13h in a search engine, or the tutorials on this site