Ed,
Yes, a bridge can theoretically do anything that a switch can. The fundamental difference is in the way the bridge and switch perform their function. The bridge is doing all in software, i.e. all traffic processing is dictated by a software running inside the operating system of the bridge. A switch performs the switching function (and possibly some more as well) using specialized hardware circuitry. The reason is clear - hardware-based switching is faster and more scalable.
The definition of a bridge you have indicated is not correct. A bridge is not defined by the number of its ports but rather by its implementation. In early days of networking, bridges have been implemented as ordinary PCs running an appropriate software to perform bridging between multiple NICs installed in the PC. Depending on the type of these NICs, the bridges could actually have performed translation between different LAN technologies and frame formats - say, between Token Ring and Ethernet. These bridges were called translational bridges. Bridges that had all ports of the same type were called transparent bridges. However, bridges were generally used only until the technology on which hardware-based switches became more cost-effective. Afterwards, switches rapidly took over.
In any case, from the functionality point of view, both bridge and switch are identical - they perform the same function and are interchangeable with respect to the services they provide. Hence, trunking, VLANs etc. may also be supported by a bridge as long as you can implement it in software (which you obviously can).
Best regards,
Peter
