WordPress MU

in which table the user information "firstname" and "last name " is saved

can anyone help me to find that

I believe that if they're defined, they're stored in the wp_usermeta table.

Yep, you got it: wp_usermeta, then first_name, last_name.

wp_usermeta is almost at the bottom of the list.

I didn't see anyone who has choosen their last name on my system so I couldn't be sure.

I had to hunt it down in the backend to find out where it was even used, so don't feel bad. :)

I started http://codex.wordpress.org/WPMU_Database_Description as its easier for a newcomer to read an consolidated summary than it is to piece together from threads dispersed over these forums.

And, if we can get newcomers to help build the descriptions then it will free up the people central to the WPMU effort so they can focus on the important issues rather than answering the same questions over and over.