First idea: The files that stutter on Linux after you edit them, did you try
to play them in XP? Does it stutter there?

Second idea: If the files stutter in XP and it is an issue with
Ubuntu/Audacity, I'm guessing that maybe you'll need to tweak the kernel so
that it loads less modules. I'm not sure how to do it off the top of my head
but there are tutorials online that show you how to maximize the kernel for
sound and video editing.

Please let us know how you progress on this.