To combine the advantages of mobile ad hoc networks (MANETs) and the Internet, we propose an approach that will integrate them into a hybrid, unified network enabling MANET nodes to have Internet connectivity regardless of their location in MANET. In order to best benefit MANET from Internet resources access, we introduce mobile gateways, which are moving around the boundary of fixed Internet gateways' coverage range, to act as an interface between MANET and the Internet. Mobile gateways are designed in a way to overcome the network architectural mismatches that exist between MANET and the Internet and widen the coverage range affixed Internet gateways. More specifically, mobile gateways are equipped with two interfaces allowing them to communicate simultaneously with MANET and the Internet using an ad hoc routing protocol and Mobile IP, respectively. Our experiments, which were conducted using the network simulator ns2, adopted Mobile IP protocol and dynamic source distance vector (DSDV) routing protocol, and showed that density and mobility of gateways as well as time-to-live of agent advertisements have an impact on the performance of the hybrid network.