Add username to the sudoers list

[mahesh]

Hello everybody

I have a big problem with my new installation of Ubuntu Server LTS:
I don't know the root password (it was not provided during the installation) and at the same time I cannot add the username to the sudoers list..
I have read already something about it, but at least people coud solve this problem as superuser (su - or sudo -i or..).
Could somebody help me out? I just would like to update my system (sudo apt-get install update..) but apparently the thing is not working as I would..
Any help would be much appreciated. Thanks in advance.

Enrico