If the program you want appears under Recommended Programs (and it should), click it, and then make sure the checkbox for "Always use the selected program to open this kind of file" is checked. Click OK and you're done. From this point on, any attempt to open that file type (not just that file) will result in Windows loading the selected program.
If the program doesn't appear, you can click Browse to locate its executable on your hard drive. That's not the easiest task in the world, but you'll need to do it if you want to reassociate that file type.
I should add that the most common file-association hassle you're likely to face is with media files: MP3s, videos, and the like not opening where you want them to. This solution works with those kinds of files as well as documents.
Force Programs to Run Full-Screen
Reader Bill has a problem with Internet Explorer 8 running in Windows XP: Every time he starts the browser, it opens in a window rather than full-screen. He has to maximize it manually every time. What a hassle!
I feel your pain, Bill. In fact, I was having the same problem with Excel 2007. Fortunately, it's a simple matter to force any program to run maximized (i.e., full-screen) when you start it. Here's how:
Right-click the program's shortcut, and then click Properties. This will open the Properties window with the Shortcut tab already selected. Click the pull-down menu next to Run and choose Maximized. Click OK .
Now, when you start that program using that shortcut, it should give you a full-screen window.