Need Macro To Create New Rows Based on Comma Separted Values in Cell

I will start with a spreadsheet where one or more of the columns has commas in the cells.
I want to be asked which column has the values that will be broken out into new rows.
Any other cells in the same row should be repeated for the new rows.
In this case, it is column B, but it can vary depending on the spreadsheet.

Before
A B
Tommy Student
Harry Bartender, Video store clerk
Sally Waitress

After
A B
Tommy Student
Harry Bartender
Harry Video store clerk
Sally Waitress[/B]