Insert block region module?

I have an idea for a new module, or maybe one already exists, or I can contribute to converting one from 5.x..?

What I want to do is add specially formatted comments that will bring in content, maybe static but preferably block regions.
So in any content body I could write this..

<!-- INSERTBLOCK 'Name' -->

or

<!-- INSERTSTATIC 'Name' -->

ie. if the module is not active then it will just hide gracefully.

I am thinking this could be implemented as an Input Format Filter. eg. it might be called Block Inserter.

Initially I would be using this module to insert ads within content like the following template customization does..
http://www.alldrupalthemes.com/blog/drupal-adsense-trick-2-adblocks-betw...

I like the idea of making a module although I can see it will be a little harder, but it will be more generic and also I would like to have fine control over the insertion position and content. eg. I will probably setup multiple ad groups (just block regions) and want to insert in multiple positions for long content, etc..

I am new to Drupal (using 6), so any advice you can give me would be much appreciated.
eg. is an Input Filter the best way to go? Can you suggest a module that would be a good start? (I was going to look at the PHP Filter)

Thanks.