To our knowledge, there is no QuickTime "plug-in" available for UNIX workstations. Instead, a QuickTime-capable "helper application" must be used. It would be impossible for us to try to catalog all the combinations of browsers and workstations out there, so you'll probably have to see your system administrator to find out how to configure helper applications on your system. (If you are the system administrator reading this, we recommend the Xanim package.)
Whatever browser and workstation you're using, though, the process should be somewhat similar to what we do here at MIT on our Athena workstations. You can take a look at those intructions for some pointers.