Lars Schmid , Sep 26, 2007; 10:11 a.m.
DNG is a digital negative format and effectively it is meant to be a universal RAW which should be used by all companies to avoid the problem that no-one can open files for new cameras. That is the idea at least. Adobe is pushing for it but many other software packages don't fully support it yet and most camera companies still use their own format.
Anyway, on Adobe's homepage search for DNG converter you will be able to download the software for free which you can use to convert you 40D RAW files into DNG. Those can then be opened in Photoshop. You won't lose any quality during the process by the way.