1: Is it possible to combine an open ended response and a Likert response in the same question?
Example: How would you describe your current residence? (1) House (2) Apartment (3) Other: Fill in (open)
Not with <likert> and <openended>, which are special types of <trial> elements. Instead you'll want to use <radiobuttons> and <textbox> elements displayed by a <surveypage>.
2: Is it possible to put more than one question on the same page?
Yes, a <surveypage> can do that. See the "Demographic survey" tutorial in the documentation for an introduction to those features.
3: Is it possible to have a question appear only if the participant answered in a certain way to a previous question?
Example:
Question 1: What is your Gender?: Male/Female
Question 2: To your knowledge, are you currently pregnant? Yes/No
The second question would only appear if the person answered "Female" to the previous question.
Yes, that's possible, but only if the respective questions are *not* located on the same <surveypage>. See http://www.millisecond.com/forums/Topic5461.aspx#5461 for examples.