Well, I am using the updated version (Adobe Audition) but many of these features remain in Cool Edit Pro. For this, I would use the "Stretch and Pitch" process. Select what you're trying to extend, and go to the "Effects" menu (may have a different title for you). Select "Stretch and Pitch" under the "Time and Pitch" category.
There, you will have several options as to how you plan on stretching the audio. One option you will have is whether or not to maintain the pitch. If you choose to maintain the current pitch, the audio might have a distorted quality. If you select the opposite, the distorted quality won't be nearly as bad, but the pitch will most definitely change. This is simply a matter of preference.