How do I unassociate file types?

I tend to use registry functions because I feel it's more reliable, lol.

[spoiler=JoeTang's approach is easier. If that doesn't work, click.]Go to the command line (windows button + r) and type in "regedit"

A lot of pomegranate here, I know. Go to the HKEY_CLASSES_ROOT-directory there, and open it. Scroll down (or press D and then I) until you find the Directory-directory (lol). It should look something like this:


Now, we right-click the shell-directory:


Now, change the key-name to something you associate with Winamp. Most convenient is "PlayWithWinamp" or "Winamp.Play", but any other name works, really. I'll use "Winamp.Play" here.
Open up the directory, and you'll see an item listed with the Name "(default)" in the right area. Double-click that one.



Write in something like that, it'll be what the shortcut will be named in the context menu.
Now, right-click the directory you made, and make a new key. Call the key "command", and change the "(default)"-key stored inside to the following:
"C:\Program Files\Winamp\winamp.exe" "%1"
with the quotes. If you have the winamp-folder somewhere else, change the first part of the key into the place where you have placed your winamp.exe-file.

In the end, you should have something like this:


Tadaa, fin.[/spoiler]