resource dll problems

Hi,

1. Is it possible to use .ico or .png bitmaps in resource dll for toolbar and ribbons and in that case under what resource type should they be added.

I have tried under ICO and PNG but they are not recognized by AutoCAD.

2. When I use .bmp in the resource dll it works for the ribbons but not for the toolbar, they show a '?'. Are there any known problems with this? 

I have added both 16x16 and 32x32 images.

3. How do I get the transparency of a .bmp to work for the ribbon?  

If I add the .ico files to the cuix file (and add .ico to the bitmap names in the commands)  it works so the cui files are correct.

Regards

Christian