It is very different. You have to watch your memory usage with pocket PC apps, along with the amount of space required.

You can use the .NET framework, but not the full one, rather a cut down version called the .NET Compact Framework. This does not have all the features the full one has, but then again neither does the pocket PC OS.

Developing is a mixed story. You should be able to use VS.NET to develop your apps but I think you need the professional edition up to do it. In VS2005 there's full support for it.