[Solved] Move HDD from older computer to newer?

Somewhat of a novice here, so thanks for your time...

Trying to help my neighbor lady with her computer. She's running XP Pro SP3, but on an older PC-- a Micron PC from 1999, with a Pentium 3 (that's right, 3) processor, and 768MB RAM.
Everything works fine, albeit a little slow. The hard drive is actually an upgraded one, not the original. It is a Western Digital EIDE, 7200rpm, 80GB.

She has come across a Dell Dimension 8200, with a Pentium 4 processor. I think it came from her son. This Dell's HD has an OEM version of XP on it.

What I wanted to do was simply swap the HDD from the Micron into the Dell, and she would benefit from the processor speed, but not get frustrated with a re-install of everything.

I can do the physical drive swap, no problem. The Dell will post, and recognize the drive. I get as far as the "We're sorry but WIndows did not exit normally last time" screen, and no matter if I choose to Start Windows Normally, or Last Known Good, or Safe Mode... the Dell just goes into a loop of rebooting (showing the Dell splash and the BIOS version, which is A09.)

I can put the HDD back into the old PC, and it boots fine. I've tried on 3 different occasions now, with the same result. FInally, I tried a differnt HDD.. one that I know came from another Dell PC. It works fine.

So... is this because the Dell's motherboard/chipset is different? If so, what can I do to make it work with the HDD from the Micron?
Or is this a Dell/Microsoft security thing to prevent the OEM drive with OEM Windows from going somewhere else? Is there any way around this? All the installations of Windows in the picture are paid for and licensed. Since this HDD is relatively new, it seems it ought to just work.

Thanks again for your time.

Question did you shut Windows the correct way (Start, Shutdown) or did you just turn it off? If you just shut off the computer that would give that error. Have you thought of installing the new drive and transferring the data on the old drive to the new.

Your swapping HDD from different computers (micron and dell) - I would boot windows in safe mode then check the event log to see what hardware that is at fault, I would install the motherboard chipset software for this and uninstall unnecessary application software. You might consider installing driver sweeper to check for hardware conflicts issues.

OK, so this morning I am now sure Windows is shutting down properly on the old (micron) PC, before I remove the HDD. But I have the smae issue when I drop it in the Dell. The Dell recognizes the drive just fine, but WIndows will not start. I can now calrify the message I get: "We apologize for the inconvenience, but Windows did not start successfully." It is definitely saying it is not starting correctly. So this leads me to believe this is not a problem with Windows shutting down properly.
Thanks again.

Best answer selected by mousemonkey.