Buttons have a Group property -- the first button with Group property set is the button that controls the start of a group. So if you have six buttons and want two groups, set the group property on the first and third buttons. Make sure the tab settings are set correctly too.
I write only MFC programs and that is very easy to set with VC++ 6.0 resource editor. I don't know how to set those manually in the *.rc file.
[edit]Sorry uman, we were typing at the same time
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