Hooking any/all 'calls'

[Kevin Little]

In Python 2.4 or 2.5, what is the easiest way to hook any and all
callables such that designated code is executed at the very start and
end of each call? (Yes, I'm trying to come up with a little debugging
tool!:) Is there a single metaclass who's "__call__" method can be
wrapped to do this?

TIA,
   -k