captain_slinky | Downgrading

Anybody have a good sollution to the probelm of downgrading from an illegal copy of Windows XP to a completely legal version of Win2k?

Here's the deal...

Bought a computer for my Mom two Christmases ago. It cam with Windows XP on it, but since it was a decomissioned DMV computer, the license on XP had expired. As soon as Mom clicke don the "Click Here to get Validated" pop-up, she's been getting the "Your computer may be at risk, not legit Microsoft Product, you are a bad person, yadda yadda yadda" message. $150 to get a legit license from Microsoft. So my Mom has just been living with the inconvenience all this time of losing her personal settings every time she shuts down and not getting any updates and the constant "Click here to resolve this problem" pop-ups.

BUT! At a garage sale a few weeks ago I found a legit, sealed retail copy of Windows 2000! Verified with the dude selling it that it was indeed a legit, unused, unregistered license for Windows 2000. He confirmed all this and explained that he was a developer who won it at a trade show years and years ago, never installed it because he's a Mac Guy.

So I paid a dollar for it.

Unfortunately, when i go to install it on my Mother's computer? It says "You already have a newer operating system on this computer so you couldn't POSSIBLY be trying to Downgrade, right?" and it cancels itself out.

Am i really going to have to back-up all my Mom's pictures and music files to whipe the hard drive and then re-install from scratch?