Time - hourly countdown

I'm trying to setup a way to calculate the hours between two dates and times. For example,

A34 - 21/07/2008 10:29 (via =NOW() formula)
&
B34 - 13/08/2008 16:00

C34 - How can display the total no of hours between them which will reduce when refreshed? It's simple to do the time calculation (one minus the other) but this only ever works for the same day (5:30 result).

What I'll be looking for is 576...etc. refreshing at each stage.

Any thoughts?

I think...

=B34-A34

Format cells - Number - Custom: [h]:mm:ss

Just [h] if you don't want the minutes and seconds.

Thanks mate - that worked nicely.