Adding User Controls on the Fly in dynamic content?

[DaveOnSEN]

Hi,
Here's what I'd like to do:

I'd like it so that I can have a web page where the page is a wrapper of
some body text in the center of the page, which is populated by a
database dip. In other words, mypage.aspx?contentid=2 gets content ID 2
from the database and renders the page with that in the middle. Ok so
far, so easy.

Here's the tricky / fun part: I'd like it so that in the dynamic
content I could mix in some macros that I'll replace on the fly with a
user control. For example:

Content ID 2:
Welcome to Dave's web page. Here's my picture: %UsersPicture%!

The parsing would locate the macro %UsersPicture% and insert a user
control of mine in that spot in the body content. Ideally there could
be several types of controls that could appear anywhere in the body
content.

How can I approach this problem? Has anyone done this?

Thank you!

David