Open the Anti-aliasing box.
Default is use application setting and "box" in the filter.
click on the filter and pick edge detect. Now at the bottom of the screen click apply. If you are having problems, hit the defaults button at the bottom of the screen, click yes on the pop-up box that appears. It only affects the app your in at the time. Now repeat the whole thing from the top.
You now have edge detect. Working with a game, if you have use application settings selected and click off 4X AA, edge detect will give you 12XAA.
If you happen to have 8XAA in the game, edge detect will give you 24XAA.
You can force the issue as well. Uncheck use application. Slide the slider all the way to the left. Alllow "box" to show up in the filter, now move the slider to 4X or 8X and then reselect edge detect. With 4X you will see 12X edge detect, with 8X you will see 24X.
Its wierd but the slider only moves in box mode. edge detect wont work for 2X or 16X.