Is there any particular reason you are using 12.10? It is a bit of a leap from debian squeeze and your install (from your other posts) doesn't sound like it went well. Why don't you install 12.04? nv is supposed to compile in that.

The Ubuntu PowerPC FAQ has links for you to read to try and get nouveau working. You need to investigate phantom outputs/mirroring or whatever other wierdness apple imposed on the card. Nobody with a 700/800 iMac has done this as far as I am aware. That is what you should be spending the time on.