Ok, so here's what I am trying to do.

I am creating a simple booking system for a meeting room. I have created a
grid of 5 rows (Monday to Friday) and 16 columns (0900 hours to 1700 hours in
half hour increments per cell). At first I thought the best way to allow
people to book was to have them select the relevant cells for the day/time
they want and then click a control button with a macro attached that simply
filled the cells with colour and merged them. Another button could be pressed
to unmerge and return to normal (cancel booking). This seems like it is
frraught with possible errors. One I have already encountered is returning
the borders to cancelled cells. If the booking is over multiple cells, no
problem. If it is just a half hour booking though the macro will not run
because it is told to border the 'inside' of the selection as well as the
outline. I'm sure more problems will arise.

I would really like to be able to have 3 drop down boxes, one for the day,
one for the start time and one for the finish time. A user could then select,
for example, (Monday) (0900) to (1200). A control button then confirms that
selection and merges/fills the releavnt cells.

Is this possible?