My initial thought when I read Julf's original post was that this might be one of those times where having a dedicated drive for the job mightn't be a bad idea. If he does that he doesn't need to be "restricted" to Linux if there's a Windows solution - chances are there's an unused XP licence code stuck to the underside of the laptop anyway!

I'm thinking along the lines of using a swappable hard drive, or a dedicated partition on the existing HD, or booting from a USB HD. The reasons I think this could be a good idea are that the DJ'ing HD needn't be tied to his current OS, and perhaps more importantly, if the day-to-day OS breaks he can still meet the DJ'ing commitments.