T-SQL How to combine multiple rows into a single row over a group

The problem:
My Data looks like this.

But i want it to look like this:

How do i do it?

Like this...

SELECT TOP 100 Percent p1.grp,

          ( SELECT comment + ',' 

              FROM combine p2

             WHERE p2.grp = p1.grp

             ORDER BY comment

               FOR XML PATH('') , TYPE).value('.[1]', 'nvarchar(max)' ) AS AllComm

      FROM combine p1

     GROUP BY grp ;

Original source and other techniques found here

http://www.projectdmx.com/tsql/rowconcatenate.aspx