I can guarantee that if there was a shortcut for grouping, Ctrl-G would not have been it, as that has always been the shortcut to the Debug/Immediate window (at least, since A2000). In A2003, there is no shortcut defined for this -- you had to do it through the menus (Format | Group).
In A2007, Grouping has been replaced with Layouts. If you search on "align controls" and then go to the first help topic ("Automatically align controls on a form"), and it will walk you through how it all works. It's substantially more versatile than the old group (it can be used to resize controls when the form resizes, for instance).
For finding features in A2007 when you're familiar with old versions of Access, you might find this Flash-based UI translator helpful. It's not perfect, as it can't translate what has been completely changed, but it can help a lot.