After the computer repairman messed around on my computer, I no longer have the Yahoo icon on the top toolbar when I have MSN homepage open.  This annoys me, and I don't know how to get it back.  He messed up several other things, but I figured out how to restore them to normal.  Can you help?

Try right clicking on the toolbar and see what options it gives you.
Was the Yahoo icon a link or what did it do?
Another possiblity is that you had a version of Internet Explorer modified by Yahoo and the tech installed a standard I.E. browser. In that case, you could simply reinstall the Yahoo browser.