Here is one way to set the default programs in Windows 7.
Click the Start Button and type "set default" and click on the "Set your default programs" link that shows up.
After you click on that, a new Window should appear. It will take a little while before the list of programs shows up. You can click on various programs on the left side to set them as Default. When you click on a particular program, it will tell you whether it's set to be the default file type for what it can handle. If you want it to open everything it can, click on the "Set this program as default" link.
If you want to decide manually what it opens, click the "Choose defaults for this program" link.
In the list that pops up, you can check the box for a file extension to set this program as the default program for that extension, or uncheck the check box for a file extension to unset this program as the default.