Date Input through to Date Range Formula for other cells

Hi All, thanks to all who have helped me in the past but i have a new crazy question.

Is there anyway i can make a formula that alters the formulas of other formulas based on inputted dates.

For example, if someone typed into field 01/05/2013 and then into another field 28/05/2013, that would then add up all of a specific range based on the date that was inputted into the other two fields.

I hope that explanation was easy enough to understand!

Thankyou in advance fellas

Is there any information i am not giving that would be useful?