What is Anti-aliasing?

Anti-aliasing is a way of smoothing the display of graphics in computers.
It makes hard lines look less hard.

http://www.widearea.co.uk/designer/anti.html
http://www6.tomshardware.com/graphic...force2-08.html
http://www.xbitlabs.com/articles/vid...rce-fx_14.html

enabling this can hit performance.

http://www.insidemacgames.com/featur...?ID=244&Page=3

This article shows the anti-aliasing settings working on a Radeon 9800.