Thanks a lot. Option "B" worked great for me. I mostly use word 2003 - it is more ergonomic for advanced use and use only one feature of word 2007 - email merge.
I was looking for a solution for a long time. All fixes I tried didn't work.
So option B - to rename "word.exe" of word 2003 to something new and to change association to that.
Ingeneous!