CPU access of shared memory on 6150/430 Chipset?

[grateful_geek]

Hi! Not sure if this is overly techical for this forum but Nvidia doesn't seem to offer anything else(including their developer site which seems mostly useless).

I'm trying to tie together XvMC and OpenGL to implement alpha-blended graphics on top of the video. In an effort to minimize unnecessary copies I'd like to know if it's possible for the CPU to access the area of system memory that's allocated for the 6150.

Also, does anyone know of a source for more technical information on the Nvidia chipset(datasheets, whitepapers, etc.)? I'd really like to get an understanding of how the pieces are playing together and the best I can come up with are high-level marketing style fluff.

Thanks in advance!
-GG