Here is a screencast to show how it works:
This goes in an xml webpart in glow:
Here is what is going on:
Line 1 includes the jQuery Library hosted by google.
We then have a simple script using the library.
Line 3 setting jQuery to noConflict, this means that we use jQuery for our main function name rather than the $ shortcut. I am not sure if I need to do this but it fixed some early experiments.
Line 5, this is where we use jQuery, we use it to add a css class of top_up to any link that links to an m4v file.