It is possible, however, it would be a long and complicated process. Here's how:
You have to locate the stylesheet for your iWeb template. Launch your site and go to view source and then find the stylesheet within the html. Put it into your browser and you should get a CSS file.
Find an existing myspace layout and then look at all of the IDs and Classes. You then have to match, or change the iWeb CSS file IDs and Classes to match those of the myspace layout. Then, you can change the look to your liking and post it into your myspace page.
Sorry if this is long and boring, but in order to accomplish what you are trying to do, this is the process. Also, you could just take the page background and browser background URL and replace the myspace CSS File background and it will look like the background of your iWeb template.