Solved. It was kind of BOIS corruption problem (?!)
I flashed an updated version of the BIOS (bug fixes not related to my troubles) and I had 2 processors, but only a single processor computer.
Win XP repair took all back.
Just a note: before I lost one processor, while I was trying to solve the USB 2.0 problem, I had a disk crash. That was probably the moment the BIOS/CMOS corrupted and the Win repair only found one CPU.
About the USB 2.0 - all is the same, I've filed a support request with ASUS. Let's wait and see.
Thanks again and have a very good 2007.