Windows 7 epic GFX lag

[Frogulis]

Windows 7 often installs microsoft versions of your graphics card driver as has been said here already you need to update it. Do not go to system and update it there! Go directly to the web site of your graphics card manufacturer and load the drivers from there, I am willing to bet that resolves the problem.

This.
You can check if you have the Microsoft driver by opening AC and looking at the console window, look for where it says "Renderer: ..."
It'll have "GDI Generic (Microsoft Corporation)" or something similar if you have the MS driver.