do you only use the stylus in PS?? or a better question would be, does it also seem "jumpy" in other programs??
if it's only wonky in PS then i'd toss my PREFs file. sometime your preference file in PS gets corrupted and make the app act all wonky. tossing the file (a new one is rebuilt next time you launch PS) often clears up your problem...

BUT, if the stylus is acting stupid and jumping around the screen even when you're out on the desktop and not even in PS, then it could be a driver issue or you getting "mixed" signals from both the mouse and the stylus.

:(
retrocity