Your other application should have it's own keyboard hooks, so disabling the standard ones is unnecessary. If you're developing the application, it's generally considered poor practice to 'steal' keyboard shortcuts that users might already expect to behave in a certain way.
That said, see:
http://technet.microsoft.com/en-us/l.../cc179143.aspx
From within Excel, you could use a macro like:
Code:
Sub Disable_Ctrl_Space()
Application.OnKey "^ ", ""
End Sub
but that might impact your other application's use of it too...