Take a look at this:
I am building this with Visual Basic using COM Technology. It allows you to use the following image formats such as JPG, PNG, GIF, BMP, TIFF or even native Photoshop PSD!, it also creates thumbnails and gives you a preview, features currently not available using standard Extension Builder. It is still under development and due to my busy schedule, I can only work on it on weekends, further more COM technology is still experimental in WWB and need Pablo to come up with a more powerful sample for implementing images.
So stayed tuned and hopefully I will have this if everything works out well.