Mikael,
Looks like you are going to have to create something. I am sure that someone out there has already done this, but unless they ante up, you are going to either have to search this tool out, or create your own.
Take a look at the file writing VIs, and the file manager. This will give you a basis on which to work. Basically, create a front panel that is similar to common file dialogs (or create your own). Then you add an enumerated type or text ring of the file extensions and descriptions (this is often neglected in windows, but great software such as Photoshop and IMAQ Vision Builder always include the description.) Speaking of which, if you have IMAQ VB, take a look at their file dialog. It's an excellent example of what you can
do, although I personally like the look of Photoshops UI.
Good luck, and be sure to let us know how you do.