There was a great thread a few months back on upholstering bucket seats in a classic with lots of hog rings and beer involved. Search the archive.
I just this weekend finished a complete upholstery on my 66 coupe (Pony interior). I was a bit intimidated at first but it was relatively easy to do and the results are great. One key is to warm the covers up in the sun for 30 minutes of so to get them nice and flexible. The buckets are a bit of a chore due to the listing wires that need attaching to give the seat its shape. It also helps to have a 50-60 pound son who can sit on the springs and make the underside attachments easier
Mustang Monthly had a few good articles:
Repair 1966 Mustang Upholstery Deluxe Interior Pony Upgrade
It really is doable, just be patience and work slowly. Good luck