This is a nutshell-type overview of how to get streaming media to play on your Linux machine. It is not intended as a step by step instruction, but merely to provide you with pointers to the software. Follow the instructions on the linked websites to install the software.
To begin with, you need to install the required tools to play media streams. Then, in a second step, you can integrate them into your browser environment to be able to seemlessly display content on sites like Apple's Movie Trailers site. Remember that software that won't work on the command line is unlikely to magically heal itself when launched from the browser.
Most content these days is served in one or more of three formats: Real Media, Quicktime, and Windows Media. We'll look at each one:
Designed from the start as being platform-independent, a player is available from Real Networks here. Download and install as per Readme file. You can then play Realmedia streams by running realplay <URL>.
Mplayer is an open-source product available from their website. It can play all kinds of media, including MP3, DVDs, and streaming videos. Download and install according to the instructions provided on the website. Some distributions have a binary package that obviates the need to compile the software yourself. Those are usually older versions, however.
Note: for optimal movie playing performance, it is imperative that your X server is compiled with X Video (Xv) support. In general, this means you will need a specific driver for your video card. XFree86 supports many models out of the box; Nvidia has drivers on their website for the GeForce cards, and ATI card owners may seek help at Gatos.
Xv needs to be enabled in the XF86Config file. When running Mplayer for the first time, pay attention to the output stating which renderer is used.
There is a graphical interface available for Mplayer, called gMplayer, which is optional. It makes Mplayer nicer to work with, but is not necessary if all you want to do is play streams from your web browser.
Mplayer needs access to special codecs to be able to play Quicktime and Windows Media streams and files. These codecs are available from the download section of the Mplayer website. The easiest way to catch them all is to download the "All in one" package and install it as per instructions.
At this point, you should be able to start Mplayer with a URL as an argument that points to a .wmv or .mov file, or to a stream e.g. on CNN.com.
The grunt work has now been done.
The browser of choice today is Mozilla or one of its decendants, like Galeon or Firefox. Since they all share the same rendering engine, they also share the same plugins, which makes things simple.
Realplayer comes with a plugin which you need to copy into Mozilla's plugin directory (usually something like /usr/lib/mozilla/plugins/. Restart the browser and type about:plugins into the location bar to see if the Realplayer plugin turns up. If it does, you're set. If it doesn't, chances are you chose the wrong plugin directory.
A really nifty Mplayer plugin can be had from another Sourceforge project. Make sure you get the correct plugin version for your Mplayer release. It may be available as a binary package, or may need to be compiled. Install per the instructions, again restart your browser, and check correct installation via the about:plugins command. The Mplayer plugin should list Windows Media and Quicktime as mime types handled by it.
Now surf on over to The Flix, turn up the volume, and impress your friends with all the latest shiny streams... ;-)