Judging by the comments on photography sites, many people have yet to upgrade Adobe Photoshop CS3 to CS4, or Lightroom 1.x to 2.x. Adobe doesn’t update the Camera Raw plug-in for older versions of Photoshop, which is a problem because updates are the only way to get support for new camera models. The same problem exists for Lightroom, where a new version of the program is required.
The Canon 50D isn’t supported in Lightroom 1.4 — only version 2.x. While the 50D is supported in Camera Raw 4.6, which means you can use it with Photoshop CS3, owners of the 5D Mark II are not so lucky: no support in Lightroom 1.4 and no support in Photoshop CS3 either; it’s supported in Camera Raw 5.2 which only works with Photoshop CS4.
To solve this problem, use the latest version of Adobe’s free DNG (Digital NeGative) converter to translate the RAW files from newer cameras into .DNG files. Lightroom 1.4 and Photoshop CS3 can open any DNG file, regardless of the original camera type. The DNG converter can be found here, and there are PC and Mac variants. It is updated at the same time as the Camera Raw plug-in for Photoshop when new camera support is added.
It works in batch mode — you point it at a directory (folder) full of RAW files and it grinds away creating DNGs in another directory. Taking the long view, DNG is probably a better file format for archiving images because it is open, unlike the proprietary camera-makers’ RAW file formats.