I'd go for C# as a language for sure. On the UI side, as someone said earlier Windows Forms is the most wide spread technology and it also has the best tool support so far (especially if you're running vs2005). WPF is a very cool UI technology so you wouldn't
be wrong to look at that either, but as I said before, the tool support isn't quite there yet as long as you're not running VS2008. You'd be even better of if you had access to the Expression suite as well. Cider (the WPF tool for VS) for VS2005 is not quite
up to par in my opinion. If you decide to go for WPF the number one book to get your hands on is a book by Adam Nathan that I can't seem to remember the name of, but it has WPF in the title.