At the Main Menu of Tactical Ops go to Tools -> System Console
In the System Console type: Preferences
When you opened the Config Screen, select Rendering -> OpenGL Support ->
An alternative method to configure these settings is modifying them manually in section [OpenGLDrv.OpenGLRenderDevice] in TacticalOps.ini
Change MaxAnisotropy to 0, 2, 4, 8 or 16
Change NumAASamples to 0, 2, 4 or 8
Change UseAA to True or False
Note: After enabling/disabling Anti Aliasing the game might crash, simply restart it and click Run Tactical Ops...