Headphone audio with Mini DisplayPort to HDMI cable I'm thinking of buying a Mini DisplayPort to HDMI cable so I can connect my MacBook Air to my PC monitor for watching iTunes movies.

However, the monitor has no audio capabilities so I wondered if anyone could tell me if I would still be able to listen to the audio via the headphone jack on the MacBook?
Yes you can, by going into the system preferences -> Sound.
Then select the tab: Output and select your output there.

As a shortcut you can ALT-click the volume icon in your top bar to quickly switch between outputs.