*Shrugs*
It's trademark infringement.
If you want to register a domain with the words "Microsoft" of any of their products in you are either:

1. Not going to be upset when you are asked to surrender it.
2. Already on good terms with Microsoft and have asked their permission first.

It is no different to me registering a domain like symantecantivirus.co.uk, adobephotoshop.uk.com or easycdcreator5.com
By doing so I'm simply asking for it.
The whole idea behine trademarks is to stop people "cyber-squatting" and the like.
If I was the owner of the domain in question I'd simply contact MS and ask them if they would be willing to pay the registration costs so that I wasn't out of pocket and then quit while I was ahead - far better than going to court against Microsoft, they cannot possibly win this one as it goes against all of the trademark rulings in the past.

I know it all does sound a little harsh.
To be honest Microsoft are not doing their reputation any good what so ever by chasing "small fry" over a very small issue.
However, I think most companies have a Zero Tollerance stance on this kind of thing - it is just this is MS so everybody gets their festive panto "booooo & Hissssss" out.
Sure it doesn't actually use the word "Microsoft" in it and the word "Window" or "Windows" really cannot be trademarked, well the OS Windows can be, but not the word.
However "Windowsxp" is a trademark and that is where this site has got into trouble.

I am not saying I particularly agree with what MS is doing in this situation, I just feel that both sides of the argument need to be looked at here and people need to imagine they are on the other side of a similar argument.
I took the time to read through some of the "Signatures" at the above URL and it was actually quite amusing.
If you disregard about 90% of the posts where people are just doing the usual "MS attacking" and those people that really don't know how domain name registration etc works these days it actually does leave about 10% that make a good argument.