Re: New Demo: VS3.0 Displacement Mapping
In a vertex shader 3.0 you can fetch texture data and use it to modify your geometry whereas in previous shaders models you can't (well there is a work around like some have mentioned where you can render your geom to a pixel buffer object and then use it to read back the vertices etc...)
The only visual difference here is that on NV40 hardware, the water mesh actually has some height to it whereas on every other card it's just the illusion of height. An illusion that gets worse when you zoom up close to the water level.
I don't know about the blockiness artifact you're reporting on your Radeon, care to post a screenshot?
You can hit F8 to save an image in TGA format to your harddrive, then you probably should use some free image software like irfanview to compress it into a JPG.