So it sounds like you're trying to connect your MacBook Pro to two things - a TV via HDMI, and to external speakers.
For the first item, connecting via HDMI, these Apple computers supply only video signals over Mini DisplayPort: MacBook Pro (late 2008), (Mid 2009), and (Early 2009). Also, on some noncompliant Mini DisplayPort to HDMI adapters, the audio signal may not be passed to the HDMI device.
This article should be helpful for connecting your computer to a TV via HDMI:
OS X Mountain Lion: Use a television as a display
For the second part, we have an article that assists with troubleshooting situations where you can’t hear sound from your speakers. The article title says OS X Lion, but it will also apply to Mountain Lion:
OS X Lion: If you can’t hear sound from your speakers