This is a fascinating art, but beware it is addictive. In order to get good results you need at least 700 of your own original artworks carefully arranged in galleries - theme, type, genre - that sort of thing.
Then it is easy with Picasa 3. As soon as you have collaged you can send the pic instantaneously by email, or upload it to a gallery with Google and Mozilla Firefox in tandem. The gallery is a SmugMug creation and it is a never-filling vault. It's pretty cool, as in one experiment I got 20,000 images on one collage. When you zoom in the clarity of the pixellated paintings is mind-blowing. If you want one send a photo and I will centre it in paintings. And like butterflies, that is free.
Hogproductions gallery was initially created to sell originals only. Just lately I got 100,000 easily viewable images of my paintings on a collage - it's too much!