We recently upgraded our systems w/the 2007 Microsoft Office version and
now
my excel files will not allow me to scroll w/my mouse scroller (the middle

roller). Any advice on how to get this working again?

Solution may depend on the OS and make,
model, of mouse.
There is usually a mouse config utility somewhere,
that allows you to swap L & R buttons, config the
pointer, set acceleration, etc.
For some mice, eg Rollerball, you need to
download the driver for your OS.