What source said they were partnering with Overdrive?
Here is another article that says they will be DRM-free, but with a digital watermark to track the purchaser:
http://www.theinquirer.net/inquirer/...-potter-ebooks
That is new information that I haven't seen anywhere else, but I've never heard of "The Inquirer" (But I have heard of the "National Enquirer"....)
eP