I would tend to agree with Cari about the foot controller/motor needing attention and Mickey2 about the upper tension needing to be taken apart, cleaned and adjusted. I've seen a few that were put together incorrectly when received so even taking pictures might not help.
While I have a few Pfaffs, I don't have any of this family of Pfaffs (260, 262, 360 and 362). A few links that might help - there is a lot of good info and some links to manuals on a couple
http://tinymicros.com/wiki/Pfaff_262_Sewing_Machine
http://www.victoriansweatshop.com/po...ff-362-8441781
http://www.victoriansweatshop.com/po...ith-my-8125238
Most bobbin cases are adjusted for normal sewing thread. I was under the impression that the upper and bobbin thread should be the same. I have seen it recommended that an extra bobbin case be purchased so that you can leave one for normal sewing and have another bobbin case so that you can 'tinker' with the tension for various threads.
Janey - Neat people never make the exciting discoveries I do.