Well I guess it depends on how you rent the equipment. If you bill by the hour, you could create Global Tasks for the piece of equipment and put the Rate that you charge for that piece of equipment in each Task. If you bill by some other increment, you could either change the Rounding on that specific entry or you could just manually round it to the nearest time (e.g. half hour, hour, etc.).
The other way you could go about it is to add it as an expense. You would create an Expenditure, for the piece of equipment, and put the hourly rate in there. Then you would just adjust the Quantity to multiply against the time units (e.g. 1 hour).
Hope that helps.