Doinf multimedia myself this year I have been told the following things:
The multimedia work must be 20 *minutes* in total. This seems to mean that it should take the marker no longer than 20 minutes to read the entire work.
The multimedia work should include elements of different media forms (i.e. video, images, sound, text... etc)
A multimedia work should explore a specific issue or topic. For instance you could (this is really cliche and bad but I think it illustrates the point pretty well) explore the concept of belonging, if you were that way inclined.
There needs to be a link to the something you have studied in any english subject from year 11 or 12 (but again, anything that's in the syllabus is fine, as long as you can link to it in some way, they have no way of knowing what modules etc that you have done when they are marking it)
Specific reference to a textual study -- english
In all honesty I have been struggling with this myself, but this is all I have learned so far.