please read the service module help pages.
the base information:
Providing ongoing service to customers is an important part of any business and one that can be a source of customer satisfaction and loyalty, in addition to revenue. However, managing and tracking service is not always easy, and Microsoft Dynamics NAV provides a set of tools to help. These tools are designed to support repair shop and field service operations, and can be used in business scenarios such as complex customer service distribution systems, industrial service environments with bills of materials, and high volume dispatching of service technicians with requirements for spare parts management.
for further details follow
msdn.microsoft.com/.../hh178221(v=nav.90).aspx
www.youtube.com/watch
So, as you can see, the service module is a module to manage customer service, repair service and so on.
For rental management you may need special contract management according national laws, payment management on monthly basis, ability to setup your assets, change management for the buildings, a.s.o.
best is, to talk to a nav partner in your region, describe your needs and suggest to extend the service module for your needs, if possible or ask for an offer for a rental customization. on the other hand, there are many nav partners, who provide ready to use rental modules.
e.g.
www.armadadynamics.com/.../eqm
www.cosmoconsult.com/.../rental
www.dynamicssouthwest.com/microsoft-dynamics-rental