Try this.

While the following isn't guaranteed to resolve all stutter symptoms on all systems, we have seen significant improvements on several computers using this method. This workaround involves partially disabling Windows Drive Indexing, a tool that speeds up Windows searches.

Disable Drive Indexing

1. Click Start
2. Click Computer*
3. Right Click your Hard Drive (typically C:) and select Properties
4. Select the General tab
5. Uncheck Allow files on this drive to have contents indexed...**
6. Click Apply
7. Select Apply changes to drive C:\ only
8. Click Ok, and then Ok again
9. Load up Diablo III and see if your performance has improved!

* = My Computer on Windows XP
** = Allow Indexing Service to index... on Windows XP

Turning off indexing to the "drive only" will still enable your Windows' searches to be quick. If you still have stuttering after this workaround, you may wish to experiment with turning off indexing to subfolders and files as well. Once you've turned indexing off for everything, the option will change to one that lets you re-enable it if need be.

In the meanwhile, I'll pass this information on to the devs so that hopefully more changes can be made on our end to reduce stuttering. Thank you!

http://us.battle.net/d3/en/forum/topic/5978349974