How does the cell change?

By the user typing in the new value--or the results of a formula?

If it's by typing, you could use data|Validation (xl2003 menus) and stop the
invalid entry.

If you change it to a warning, then you could use format|conditional formatting
to show the value in red.

If the value changes via a formula (or by typing), you could use
format|Conditional formatting and a helper cell:

=if(a1<=200,"","Error too large")

Format this cell in big bold red letters to make it noticeable.

delete automatically wrote:

Make a cell font red if number is greater than 200 and have a message pop up
saying (you have exceeded the number of hours allowed).

--

Dave Peterson