The bandwidth command in Cisco doesn't 'set' the bandwidth, it merely allows routing protocols aware of bandwidth to generate the metric (OSPF, EIGRP etc) and allows accurate statistics to be generated. It is also referenced by QoS polices that are applied to interfaces - i.e. if the interface is 1024Kbps then you can apply a policy that is based around 1536Kbps.
If you are clocking your own interfaces then the 'clock rate' command is used to 'set' the bandwidth, the bandwidth command would be applied to tell the router the speed so it can generate accurate routing metrics etc.
With regards to what the equivelent commands for a 3Com router are, it depends on what router it is.
Andy