Somehow your post got into the Community Canvas which is for discussion about the Tableau forums, so the folks who monitor the forums for questions to answer missed this one.
If the column in Excel is formatted as a date, then Tableau should bring that in just fine. So I'm guessing that the "2011 Q1" is a string, therefore you're going to need to turn that into a date in Tableau via some string manipulation. A formula like this where [Date] is replaced by our date field should work:
DATE(LEFT([Date],4) + "-" + STR(INT(RIGHT([Date],1))*3-2) + "-1")