I have a Microsoft Optical Desktop Elite Keyboard and Mouse for Bluetooth, and wanted to get them working on my newly installed Ubuntu 7.04 Feisty Fawn desktop. (This was my choice after the adventure of Windows Vista deciding it was not Genuine 1 1/2 months after install, even though it was.) See this article for the details.
I found the basics of this article on the Ubuntu forums, but found that I needed to adapt it a bit. So here is that article, with my changes/additions.