I know it is not a normal practice for someone to deploy 2010 map to 2006 server but I have no choice. The questions i have is "Can I deploy a 2010 map to 2006 R2 server"? It seemed to me that since they are both btm files, the only difference between 2010 and 2006 mapper is in the UI, not the generated maps. But, I'm not sure if that is true, and before I can deploy this to production server, I need to be sure.
Thanks for the answer.
After some research and experiment, I figured it out. Apparently, the btm file used by the 2006 mapper and 2010 mapper are both the same format. So, copying myMap.btm file from a 2010 project and adding (existing item) to the 2006 project did the trick. I am almost sure this will work coversely too although I have not tried it. Anyways, I compiled the project, and got my 2006 map dlls, and my boss was happy :)