No problem.
Here's what you do:
1. Go to your home page on myspace.
2. Click on "Upload/Change Photos".
3. Select which picture you want to add the second image to.
4. Under that picture, click "add caption".
5. On your computer, have your picture on the desktop (where you have icons and stuff, where you can see it).
6. Go to
http://tinypic.com, and upload your picture onto there.
7. Go back to your myspace and in the caption section, copy&paste the picture's URL (the one you just uploaded). The URL will look something like "http://tinypic.com/somethingsomething".
8. When you're done copy&pasting, click "submit".
Then the picture should show in the caption section.