I've had a similar problem in that Canon do a RAW image plugin for Vista but only for 32bit.
Makes me wonder why Microsnot produce 64bit software at all.
I now use Fastone veiwer and have come to quite like it, however it does grieve me that we seem to have taken a backwards step on what was supposed to be an operating system aimed at multimedia.
Have a look here
FastStone Image Viewer - Powerful and Intuitive Photo Viewer, Editor and Batch Converter