I'd noticed a couple of comments on this blog, and some others, around the setup steps required for Oracle BI Publisher and Discoverer integration. Setting this up requires quite a few steps in the 10.1.2.2.0 release of Discoverer, which should be made a lot easier in the 10.2.0.3 release, but for now you have to apply a few patches and go through some security configuration steps. One bit that seems to be catching people out is the requirement to configure BI Publisher to use OID as it's security method, I don't think this is in the main docs but it won't work without it.
Anyway, I was discussing this with Mike Durran, the Discoverer Product Manager, and Oracle have come up with a detailed setup document for BI Publisher and Discoverer integration, a collaborative effort between a few consultants, which they've kindly agreed to allow me to host on this site - you can download it here. It's got lots of screenshots, explanations and so on, and whilst I've not gone through it myself (I've already got it up and running) it does seem to cover off all the required parts, including the BI Publisher / OID setup step. Anyway, download a copy if you're getting this up and running, it should cover off all the steps you need.