asterisk users - Aug 2004 - Dial/Zap doesn't work

Hi,
    I'm trying to dial in from one phone and give it access to another 
line (ie incoming on zap/1 and outgoing on zap/2)...  how can I transfer 
the call from channel 1 and give it the dial tone on channel 2?  I can 
use dial but that takes a phone number, which I want the user to be able 
to select.

thanks
Imran