Chosen Answer:
You need to have the right permissions to do this.
1. Go to “Site Actions” > “Edit Page”
2. On the “Site Image” webpart, click the edit dropdown that looks like “edit v” Then click “Modify Shared Webpart”
3. In the “test link”, put the url of the image you want. It could be a real address like http://www.somesite.com/images/someimage.gif. If you want this to be an internal link, you have to put the image in the images directory in the 12 hive, which on the server is C:\Program Files\Common Files\Microsoft Shared\web server extensions\TEMPLATE\IMAGES (for this, you will need server level access, which most editors don’t have)
by: xdwcpsd
on: 10th February 09