How would you write a formula that looked up part of its cell restraints?

For instance €“ if you have a set of formulas like:

=SUM(Timesheet!C32:C396)
=SUM(Timesheet!D32:D396)
=SUM(Timesheet!E32:E396)
=SUM(Timesheet!H32:H396)/8
and so forth.

Where the Column designation stays the same but the beginning and ending
numbers change based off of what period I decide to look at.
Is it possible to write a formula that references the number portion of the
cell designations from a separate cell?

For instance:

=SUM(Timesheet!C{=A5):C{=A6})
=SUM(Timesheet!D{=A5): D{=A6})
=SUM(Timesheet!E{=A5):E{=A6})
=SUM(Timesheet!H{=A5):H{=A6})/8

I ran into this situation, just changed all the numbers to fit the periods I
was wanting to view from my continually growing data page but was wondering
if there was an easier method.

--
Bill H.