To access file associations, go Control Panel->Programs->Default Programs->Set Associations. Then, for each file type (JPEG, GIF, TIFF, etc) select the extension and click the Change Program button. If Photoshop isn't listed you can browse for it. From then on whenever you double-click or otherwise attempt to open a photo of that type it will automatically open in Photoshop instead of Snapfire.

Hope this helps,