I actually just built a new machine Monday. The only thing I kept out of the Dell I had was the processor. I used the copy of Windows that Dell gave me. It would not activate. I called Microsoft and they had me activated in 5 minutes.
I'd like to know where Dell draws the line. I have a massive stack of OS CDs from Dell that are BIOS-locked and will not run the setup program on anything but a Dell. They range from Win2k without any service packs all the way through XP SP2, so this is not a new thing. But I keep seeing people that can install theirs anywhere.