xp, cuda 3.0, vs2008 can't compile

I am struggling for days now to get some old code running (must admit software is kind of new for me, have hardware background). I can run the examples, so I thought I take a working example and change the source files to my own files.
I get the message now that threadIdx is an undeclared identifier
-I included cuda.h
-I have a build rule (do you really have to edit the project file manually to add a build rule in a new project)
-my files are named .cu

When I right click on the cu file and compile, it works fine, but when I compile the main file which includes this file, I get this message.
Anyone an idea of what I do wrong?

Is there any basic documentation about how to start a project? I am not so interested yet in the memory coalescing and different types of memory, etc. My main problem is in compiling stuff. If I repartition, I have to struggle half a day to get things working again. I feel I am going about it all the wrong way, since I am so amazingly unproductive.

P.S. I think I get what the problem is: you can not just include a .cu file in you c code. You can probably call host functions in your cu file from c, only through some EXTERN mechanism.