To start let me first explain the issue. The first problem I noticed with 7 is that when I double click on a .gif it will not open it in Photo Viewer like any other image format. But it doesn't stop there. Not only will it not properly open on double clicking the file but you cannot simply right click it and choose "open with" since Photo Viewer will NOT appear in the list when right clicking a .gif so this is an issue because Photo Viewer is not a standalone application. There is no .exe file to choose when manually browsing for it.
Here is the proper solution:
1. Right click on a .gif image.
2. Choose "open with"
3. Click "browse"
4. Make sure you select "all files" from the drop down in the lower right side.
5. Navigate to C:\Windows
6. In the search box type in PhotoViewer.dll
7. Make sure you check the box "always open with" To associate the .gif extension with PhotoViewer.dll
Summary: Now when you double click a .gif it will just open the way it should in Photo Viewer as a preview.