InfoPath Dev

I'm still very green with InfoPath but the more I use it the more I like it.  Would like assistance on the following. 

I am trying to calculate the number of calendar days based upon three fields "ServiceFromDate", "ServiceThruDate", and "TotalServiceDays".  As an example, if the service from date is 08/01/11 and the service thru date is 08/07/11, I need the total service days field to reflect 7 days.

Alternatively, I need to calculate the duration of service provided to a client in a different portion of the form with the three fields "ServiceStartTime", "ServiceEndTime", and "TotalServiceTime".  As an example, if the service start time is 10:00 and the service end time is 11:30, I need the total service time field to reflect 1.5 hours.

Any advise would be appreciated.

Check out this site

http://alecpojidaev.wordpress.com/2008/12/30/infopath-codeless-programming-walkthrough-2/

I'm attaching a form with the idea from that blog.

That's exactly what I wanted!  Thanks.  Would the same basic function work for time?

 Thanks again.

You would most likely have to fiddle around with the formula for time, but I think that example will give you a general idea of how to get it done.