how to replace the window on driver's side

This one is not always for the faint of heart. You'll deal with tight spaces and sometimes fierce resistance. It's also a bit complex for this medium. Seek out a Chilton's (local library, with a Mustang you'll probably be able to peruse a copy at Borders or Barnes and Noble, or e-bay) and size up the job before you decided to attempt it. If you decide to seek professional help, look for a junk yard with a garage first. That may be your cheapest out here and they can help find a window if you still need one. After that look for a Mom and Pop body shop. Good luck!