AA is Antialiasing and AF is for Anistropic Filtering, They are used primarily to smooth the look of the video output and make things look crisper and sharper at higher resolutions.
they are enabled in your windows video card settings generally you have options that you can set to 2x 4x 8x 16x in AA and 2x 4x and 8xS i think in AF on my Nvideo 6600Gt video card settings I have a special area to set these
here's a link to a review that has some explainations