My honest opinion - take a look at the VB code in the example I linked to - you will need to modify it slightly to include your watermark, but that is probably the simplest way of doing it.

Note though that i haven't used that source code at all so I can't necessarily give you any great help with it.

I have probably got some example code of how to take a gridview and build the contents into an HTML table but its on my old laptop - I will see if I can dig it out.