Apps :: How do I associate an application with something?

It's SO ANNOYING when I try to open a file, and I get a dialog box asking for the directory under which the application for opening it lies.

How do I avoid this or deal with this? Is there a place where I can always count on a particular application being located (pdf reader, Abiword, gnumeric, xmms, etc.)?

In what program?

Usually the executables can be found in the PATH environmental variable.

usually they are in /bin, /usr/bin, or /usr/local/bin..

original here.