Rests, just like notes, need to have the duration set first.  You are getting quarter notes, because that's the default duration when you open Noteworthy Composer.

For rests, just do the following:

Whole note rest:  Press "1", then space bar
Half note rest:  Press "2", then space bar
Quarter note rest:  Press "3", then space bar
Eighth note rest:  Press "4", then space bar
Sixteenth note rest:  Press "5", then space bar
Thirty-second note rest:  Press "6", then space bar

Likewise for notes, press the same corresponding number, then press ENTER after positioning the cursor where you want the note.

If you want sixty-fourth note rests (or notes), you'll have to select it from the tool bar (there's not shortcut key).

Hope this helps,

John