The only experience I have so far with a touchscreen interface was one where everything was custom drawn, and I get the feeling it's not the most efficient way of doing it (even the most basic layout change is hell to make). I know plenty of GUI toolkits intended at keyboard & mouse interfaces, but can you advise something suited for touchscreens? Target platform is Windows, but cross-platform would be nice.
Check out the Windows Presentation Foundation (WPF). It uses XML (XAML) to define the interface and it is therefore quite easy to create an interface which would be easy to use with the touchscreen.
.NET 3.0 required.