If you purchase a package, which is a PC with XP pre-installed as an OEM at a bargain price, then changing the main board may result in your not being able to reactivate XP - although I have not yet found it to be so. Perhaps it's advertising hype?

I have recently changed boards on Advent (PCWorld own brand) and HP PCs for people.

I was able to source a similar MSI board to the original Advent had used, so it booted from the hard drive. Then it insisted on activation. I tried to do it online, but it refused. So I rang Micro$haft and explained. They asked me for the product key from the sticker on the case, gave me a code to input manually, and it was fine.

I couldn't find a near match for the HP board (also an MSI), so put in a completely different board and processor. It wouldn't boot, of course, so I ran an OEM copy of an XP disk (the system restore wouldn't recognise the board), and used the code from the case sticker. It installed and activated successfully, and updates correctly.

Like you, I still have Win95, Win98 and WinME machines for testing websites, etc. I also have a Win 3.11 machine, too! Somewhere I also have a working XT running MSDOS 3.3! It has a 30Mb hard drive and 1Mb of memory...!!

Maybe the second of the two examples isn't strictly within the terms of the licence agreement...