You need the Omega drivers, I believe, which will run on the Mobility RADEON chipsets. They *should* work, but there are no guarantees. Alternatively, you can wait until your laptop manufacturer releases newer drivers.
As for your other question, I'm not sure you can do that with the current DDR/DDR2 standards; there may not be enough address pins. You'd also have a tough time fitting all the chips onto one DIMM! Plus, 32-bit OSes can't address more than 4GB anyway without some serious hacks (like Windows' PAE).