Hi, I hope this will help you on your way...
Open your admin panel and got to tools, Define Pages Editor.
The page you want to touch is "define_main_page"
once there you can add your picture in 2 ways:
1. have a image manager contribution installed, or
2. inser following code:
Code:
<p align="center"><img height="height of image" alt="Alternate name (for when the picture doesn't come up)" hspace="0" src="images/*.gif or jpg" width="572" align="baseline" border="0" /></p>
Any bold text is your own info, the reason I use the relative place of the picture is so that it works with my SSL and deosnt give an error. You can use an HTML link for that but if you have SSL it will ask the customer if they want to see both secure and insecure data.
Hope this helps, message me if you need more help.