A September 16, 2004 article on the Japanese-language web site Nikkei Electronics Online states that the CMOS image sensor in the upcoming D2X digital SLR is being manufactured for Nikon by Sony.
The article, which requires free member registration to view (and if you can't read the language, and don't reside in Japan, registering is nearly impossible), also notes that Nikon plans to manufacture 8000 cameras per month.
A source for this information doesn't appear to be cited in the article, which otherwise is a brief technical summary of the D2X's sensor-related features.
In addition, an August 2004 document included in the financial information Sony released for fiscal year 2004 notes that "Sony has almost completed work on a CMOS image sensor that produces a higher-quality picture." Though Nikon isn't mentioned specifically in the document, which is entitled The Future of Key Components (download the PDF here), it seems likely that this reference is to the D2X's sensor.
Thanks to Simon Dai for bringing the Nikkei Electronics Online article to our attention, and to John Roberts for tracking down The Future of Key Components PDF on the Sony web site.
Nikkei Electronics Online article