I can't get the game to start due to an error message saying d3dx9_35.dll is missing. Do I have to download the game again? or is there an easier way to fix?

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=3b170b25-abab-4bc3-ae91-50ceb6d8fa8d&pf=true

Download and install this (extract, run dxsetup.exe or whatever it's called).

I had this problem too when I tried the demo to see if I could play the game. I think there should be some sticky or something about this because alot of people getting the game now will probably have windows 7 and thus have later versions of direct x.

google the dll ftle download and put it in the main witcher file worked great for me

I think is safer to install the latest directx altogether.
There is a similar topic here about this issue.