Upload to a site like Photobucket. Select the links which say "for ebay" and copy them.
Type your advert as usual on ebay and when you are done. Click "switch to html view" which is at the top of the text entry box. This will show everything that you have just typed in html. Copy the links from Photobucket into this view.
Switch back to normal view to check that they are positioned right, job done.