To set them up in Windows, click Start ⇒ Settings ⇒ Control Panel ⇒ Folder Options ⇒ File Types. See the more detailed instructions on setting up the *.jnlp association. In Windows W2K/XP/W2K3/Vista you can now sort the list by extension or filetype by clicking on the heading. You commonly set up edit for example to use your editor in preference to wordpad for a given extension, e.g.

There are also another set of associations in your browser between extensions, MIME types and programs to deal with those documents.

In Vista, there is a simple editor for associating extensions with programs. it does not handle MIME types. Click Start ⇒ Default Programs (on right) ⇒ associate a file or protocol with a program.

1. Start
2. Default Programs (on right)
3. Associate a file type or protocol with a program

java.exe vs javaw.exe

Vista no longer lets you configure the all the associations, e.g. open, edit and print. There is a way around that, using Creative Element Power Tools, other than manually modifying the registry.