Photoshop CS3 beta trial...
http://labs.adobe.com/technologies/photoshopcs3/ (you must create a login with email there)
the installation routine will ask you to install various other programs, you can uncheck all (not needed)
After installation, go to the AMT folder and rename application.sif to application.sif_
(if you want to get rid of the annoying "register now" popup)
Note that PS CS3 will change most of your image file extensions, so all files will now open with Photoshop.
You can undo this by opening an explorer window, clicking extras->folder options->file types->select for example jpg->click change-> select the standard windows image viewer