Microsoft has built in support for OSX into its HD Photo (also known as Windows Media Photo) plug-in for Photoshop (which has been released in beta).
The beta supports both Photoshop CS2 and CS3 running on OS X 10.4 (Tiger). It supports either version of Photoshop on both Intel and PPC Mac systems.
Microsoft's Bill Crow, product manager for HD Photo,blogged that:
"One very cool feature with the Mac version is support for thumbnails in the OS X finder. OS X doesn't currently HD Photo as a native format. However, whenever Photoshop writes and HD Photo file, it also creates a thumbnail on the resource fork in a compatible format for OS X. The result is great looking thumbnails for HD Photo files in Finder."
HD Photo Plug-in for Photoshop - OS X can be downloaded here.