Is there a keyboard shortcut in outlook 2007 to flag an email instead of having to mouse click the little flag?
You can just press Ctr-Shift-G and then hit Enter.
Edit: You can also just press Insert if you just want to mark it with the default flag. Additionally, pressing Insert on an already flagged item marks it as completed.
Autohotkey could do it!
What you want to do is install AHK, then use the bundled Window Spy to find out the position of the button. Then you'd use something like this:
edit: djhowell says you can use Control+Shift+G, then return. In this case your hotkey would be:
Keep it simple!