There is nice feature in Windows Vista / 7 (and WinXP SP3) called "image codecs". This little think allows user to install "plugins" for rendering non-default images (and thumbnails). This is especially needed by photographers working with RAWs.
But, there is one big problem... Either Canon, nor Nikon won't us to work with 64bit Windows?!? Or at least they don't want to provide image codecs for their RAWs for 64bit Windows :( And Adobe with their DNG also isn't supporting 64bit Windows. Photoshop is 64bit ready since CS4 version (now, there is CS5) and Lightroom is 64bit ready since Lightroom 2 (current version is 3.0). So, we have 64bit photo software for at least 2 years, but still no 64bit image codecs? Photoshop / Lightroom (and others) has to render images and thumbs on 64bit Windows, so why is there no image codec? Adobe? Canon? Nikon?
On the other side, there are several 3th party image codecs that can handle RAWs and DNGs even on 64bit OS... But, you have to pay for them. There is problem with paying the software, but image codecs should be provided by "owner" of the image (RAW) type.
Right now, there is one very good solution for $9.99 - http://www.fastpictureviewer.com/codecs/
(but, it is limited time offer).
What are you using as image codec on 64bit Windows (if you go 64bit way)?
Windows 7 is the first Microsoft's OS with more 64bit installations than 32bit. This is the trend... 32bit is getting old and computers are moving to 64bit world... Photographers can and will enjoy benefits of more RAM... Currently I have 8GB and thinking about upgrading to 16GB. With 32bit OS you are limited to 4GB (including video RAM). Working with modern RAWs or big panoramas in Lightroom / Photoshop needs more RAM, RAM is cheap, so why not to switch? I switched from WinXP to Win Vista x64 few years ago and I'm very happy since then.