1.-First create a code with threads
2.- Load the debug bar.
3.-In the debug bar exists 5 buttons ,use the button show thread in source.
4.-Run your code "Remember mark a breakpoint to debug the thread".
5.-When you are in debug mode, you are able to load
Parallel Stacks=Ctrl+shift+d , s
Menu Debug ---windows --Paralel Stacks
Check this link
http://beyondrelational.com/blogs/hima/archive/2010/08/08/vs2010-parallel-tasks-debugging-enhancement-in-vs2010.aspxhttp://www.danielmoth.com/Blog/Parallel-Stacks-Another-New-VS2010-Debugger-Window.aspx