I haven't downloaded it, but your Url class sounds suspiciously like it does everything that the built-in Uri() class does anyway? If so, why write it?

Both classes are very similar indeed. In fact, the Url class was one of the first classes I wrote in .NET and at that time I wasn't aware of the Uri class.
However if you need something that the Uri class doesn't offer, the Url class is a good starting point.