Let's see...
... Oldest to newest.
One 9.5 year old dell Inspiron 1300. Currently will not run more then 1 program with out freezing solid. Primarily get used to run non interactive programs, (it runs christmas light shows).This computer is indestructible, it has been dropped so many times, run in -40 weather, run in conditions of extreme dust, I have no idea how it even turns on.
Runs Xp professional.
One 5 year old dell vostro. Piece-0-crap right from the factory, thankfully I got it free.
This computer actually functions properly.
Runs Xp.
Now my pride and joy, my custom built PC.
I had it built for me by a shop, however it cost the same as if I built it myself (they get a wholesale price)
Do not ask me what's in it, I have no idea.
This runs Windows 7.
The first two are laptops btw.