Normally, the Windows Image and Fax Viewer will steal associations from other image viewers, such as AcdSee, so that when you double-click a jpeg (for example) it is opened with WIFV. To prevent this irritating behavior, delete the subkey inside HKCR\SystemFileAssociations\image\ShellEx\ContextMenuHandlers which I believe was named Preview (before I deleted it, that is).
-=Marcus
Prevent Image and Fax Viewer from Stealing Associations
Posted in Windows XP by Community Submission