fmlovetm3 What world(s) are you playing in, and how does the game run in Sunset Valley? What expansion packs have you installed?
Have you taken steps to limit your in-game framerates, and have you confirmed that the limit is being respected? You can bring up the cheats console (ctrl-shift-C) and enter fps on to show an fps counter in the upper-right corner of the screen.
Please also provide a dxdiag. Click Windows key-R, enter dxdiag in the run box, wait for the scan to finish, click "Save all information," and save the file to your desktop. From there, you can attach it to a reply using the paper clip (Attachment) icon included with the other formatting buttons.
