Right click on desktop & open it.
Select Manage 3D settings, then click on the Program Settings tab.
Either select ET from the dropdown list, or if it doesn't appear, click add, and browse to the directory.
Here you can finally force the antialiasing. Set Mode to override application settings. Setting, set to whatever you want (you want your fps first, but fuck the jaggies) I have mine set to the highest settings & still hold 125fps.