There are a number of problems that can cause this.
In Windows7, there are mouse lag problems with various fixes.
RAM and video card RAM insufficiency can do this also.
There are a number of issues with old mouse drivers and old video card drivers.
Some computer mouses (?mice?) have gaming modes.
Suggest:
Get more RAM up to 4G.B.
Use Game Booster or AlacrityPC to free up RAM and turn off background processes and applications that are not needed for the game.
Make sure you have the latest drivers for your video card and mouse software
Mess around with you mouse settings in control panel
Mess around with your video card settings, especially with the render ahead settings.
As noted above, if your frame rate falls with heavy graphic loads, you might have to set some of the game options to low or off.
Some people have found that the video sync settings make a difference.
Finally, Welcome Aboard!
