Music stutters when opening applications

> I had this problem before but for the life of me I cant remember how to fix it
>
> When Im listening to music from the hard drive via Itunes the songs stutter
> when I first open Itunes or stutters if i open another application. It
> happens too when my hard drive is doing something, I know this can be
> rectified but i cannot remember how
>
> XP Home edition
> I tunes V6
> 2.66 ghz
> P4
>
> Any help is much appreciated