I did an upgrade on a Compaq Presario from NT4 Workstation to 2000 Professional. I had two problems.
1) the SoundMax audio drivers for NT4 did not convert during the upgrade. When I was done, I had no sound. I found an article on Compaq's web site about this. All I had to do was remove the existing SoundMax drivers and then download the Win2K version.
2) When I do a Shutdown -> Restart, I always get a BSOD right when the pc is about to be turned off. There is a problem with the .SYS file that controls the power cycling sequence. I have not found a solution for this yet. If you just do a Shutdown, it is ok; if I do the Restart it BSODs. I think I looked one day on Compaq's site but did not find anything useful.
Other than these 2 gotchas, my Compaq is running fine.
Hope this helps