I found this from a link at Wired News.
What it does is make your Windows XP machine look and behave more like a Mac. Lots of Mac users have told me that they can function better in the Mac environment because it suits how they work better. If you think you might be one of those or are just curious, download the free trial of TopDesk and give it a whirl. Should you decide to keep it, the price is only $10 (USD). It's definitely worth a whirl. I rather liked the trial.