Installed the desktop version 9.04. But I can't login as root.

You can't login as root in Ubuntu, actually, however, a part of guide on the link below can be helpful, it has instructions on enabling the root account.
https://help.ubuntu.com/community/RootSudo

Thanks 13thSlayer

Logging in as root is a really stupid idea too. you will be running all apps as root (like web browser and irc client etc) which if captured will give the attacker root access, using the system as user and using sudo is far more secure.

Hi :)

In support of what ActionParsnip says
https://help.ubuntu.com/community/RootSudo

In Windows you are forced into being Root a significant and unnecessary amount of the time, even for running fairly basic applications. As a result Windows is always having security issues and vulnerabilities exploited. While they keep on saying their system is "more secure now" we can see entire industries growing up to help mitigate against the flaws they build into their system. Linux is designed to be secure, you really do not need to run as Root and doing so is dangerous
https://help.ubuntu.com/community/Antivirus
http://librenix.com/?inode=21

Good luck and regards from
Tom :)

Thanks. The problem has solbed.

Hi :)

Thanks, sorry i get all work-up about this issue. A lot of new users from a Windows background try this and then wander why problems start happening. Now i recognise your name i realise that you were probably saving all admin tasks for a regular session as Root to batch everything to a short session. Which does make a lot of sense

Apols and regards from
Tom :

Thanks, Tom *l.