Just installed the Microsoft Camera Codec Pack for Windows 7.
I can now see my RAW images in Explorer, I don't have to keep going to Lightroom, just to look at an image. http://www.microsoft.com/download/en/details.aspx?id=26829
It does what it says on the tin, although it does take some processing power, when converting all the images. On my Core i7 laptop, a folder with 182 20MB RAWs from my EOS550D took a couple of minutes to cache.
The good news is, that the codecs seem to be mutli-threading enabled, it is using 6 cores at the moment.