You need to set the default. Usually this is easiest done by right clicking on the picture file (using explorer) and selecting 'open with'. Then you can choose Photo Gallery and tick the box saying always use (or words to that effect). That should do it.
Ta muchly both. Sadly, neither works. Look at SA's link it appears to be a problem attached with Windows Live Essentials, will have to see if I need anything form that before considering an Uninstall, which appears to solve the problem.
A lot of people will be falling about laughing when they read that you're using Windows Photo Gallery. Like almost everything from Microsoft, it's absolute rubbish. The most popular image viewing (and editing) program is probably Irfanview, which is infinitely better than Windows Photo Gallery:
http://www.irfanview.com/