I know that MS/Canon used to provide RAW viewing capability back in 2005, but there hasn't been much in the way of compatibility updates since then.
I've just been using Bridge to view my Canon RAW (CR2) files but I tried this free utility today in Explorer and it works very well.
I know this isn't a big deal for many, but if it helps anyone that still wants to see RAW files (from many mfgs) in XP explorer, it will have done it's job. I don't know if it will show CRW files in Vista, so I'll have to wait until I'm back in the studio to try it (Canon doesn't support viewing CRW in Vista).