I'd like to enter running times in minutes and seconds into Excel 2003 to
keep track of it.

I can make a mask such as 00":"00 but then if I enter 16:40, Excel sees it
as 1640 rather than 16 minutes and 40 seconds.

How do I get Excel to format my time as mm:ss and see it as 16 minutes and
40 seconds rather than as a date and time?

I'd like to be able to use formulas and graphs with this, so Excel needs to
view it as minutes and seconds as well as just display it visually.