Vain : Nice effect, really

Multisampling is relatively simple : Lets say your resolution is xRes*yRes, you render your scene on a xRes*2, yRes*2 sized buffer and then render that buffer on the screen with a box filter (you merge 4 pixels from the multisample buffer to 1 pixel in the screen buffer), it'll do sort of an anti aliasing on all screen (graphics improvement is huge !!).
However, it can be made in software but with a non-interactive framerate (Maybe Am I wrong ? I'll let the masters of optimization tell about it

) or it can be made in hardware (don't know how though :S)