<p>Upon opening Transmission for the first time, a Mac OS X dialogue box should appear asking if you will allow Transmission to receive incoming connections. Click Accept.
<p>If this doesn't happen, you can add Transmission to Leopard's firewall manually:
<divsummary="To do this"id="taskbox">
<ol>
<li>Open System Prefs >> Security >> Firewall. Make sure "Set access for specific services and applications" is selected.</li>
<li>Click the "+" button and select Transmission from you Applications folder. </li>
<li>Make sure the pull down menu is set to "Allow incoming connections".