You'd have to create your collage in an image editor such as photoshop. You can download a free 30 day trial from Adobe, alternatively there is a program called GIMP which is free to download and use.
- Copy and paste your own images into the photoshop/gimp document and arrange however you like. (there are loads of tutorials if you google it)
- Save as a .jpg image
- Upload to a site like Flickr or Photobucket and copy the new url of the image over the ****** in the code I'm about to paste.
MAKE SURE IT'S THE FULL URL ie: Http://www. NOT JUST www.
You can make changes to any part of the page by downloading the style sheet, making your changes and pasting it back in again.
Good Luck! :)