Trouble with file association

Microsoft Windows XP

I installed an image viewer program to view my digital photo .jpg files. According to the list under the File Types option of Explorer's Folder Options, .jpg files are associated with this program. However, whenever I double click on a .jpg file in explorer, it opens with Windows Picture Viewer. I've tried associating .jpg files with Photoshop, but the same thing happens. Is there a way to dissociate these files from Picture Viewer so that I can open them with the other program?

Click Start/Run/ "regsvr32 /u shimgvw"
*Might* cause some side-effects. If you find any problems later, re-register it "regsvr32 shimgvw"