Sharon, you have probably checked this already, but it sounds like this may be similiar to the machine your friend has.
http://www.kenquilt.com/index.php?main_page=product_music_info&cPath=1&products_id=473
That size would be considered a mid-arm, and you would definitely be limited due to the small throat space. (My Handi-Quilter is 16", and there are times when I really wish I had more space.)
Would it be possible for you to test drive the machine before you commit? The machine is probably OK, but make sure that the entire set-up is sturdy and operates smoothly. It sounds like it might be a really economical way to test the waters of the long-arm world!