Excel & Time Calculations

Using Excel 97 how can I calculate time?
I’m using the following cells:

Start Time cell:
End Time cell:
Total time:

Example1: I Start at 10:00am and End at 2:00pm. How do I calculate an answer of 4:00 hrs in the Total cell?

Example2: What if I span a day? I Start at 8:00pm Monday and End at 1:00am Tuesday. How do I calculate an answer of 5:00 hrs?

Thank you.