I have this old computer kicking around under my desk gathering dust, and I'm trying to figure out what to do with it, when I thought about using it in the garage..

So - what sort of software would be good (other than the o/s - it runs XP ATM, but it could run 7 at a push)?
I don't know what's available for the amateur mechanic, or even what's worthwile installing, so any suggestions would be welcome! The 4th Gen manual will of course go on, but I'd like it to be useful for something else than just a PDF viewer..
Also, are there any worthwhile diagnostic connections I could get to plug into the various cars we own? ('93 4th Gen, BMW E36 318ti, '54 plate Picasso)
Thanks for any advice!
Cheers
Doug