Well I had the same problem and it was not the fuses. Some of the wires in the harness going to the rear doors were broken,maybe due to the tight angle it is in. It started off with the rear speakers dying and then the windows stopped working.
In my case the broken wires somehow managed to cause a short circuit that blew the fuse number 17 (30 AMPs). Subsequent tries to replace the fuse failed until I rewired the harness, which takes a lot of time and a lot more patience.
If you are interested, here is page where the actually rewire the harness. The downside is that it's in german so you might hat to run it though some translation tool.
http://www.langzeittest.de/opel-zafira/technik/kabelbaum-hintertuer.php
Jack, July 2009
