In order to post to Twitter and Present.ly simulatenously, you must first store your Twitter account information by clicking on Settings at the top of the page and then the Services tab.

Once you are on the Services page, you simply enter your Twitter username and password in the specified box.

After your account information is saved, you're ready to post to Twitter! All you need to do in order to post to Twitter and Present.ly simultaneously is prefix your update text with "t!". For example:

t! Working on the new Present.ly knowledge base.

This will appear in your stream like a normal update but with an indication that it was cross-posted to Twitter. Your colleagues will then be able to click through to see your Twitter account.