Strange installation problem

[eluser]ryantxr[/eluser]
[quote author="snaggy" date="1187954389"]It doesn't work even without persisting connection..

Can you tell me what modules I need? I have installed through synaptic package manager php5-mysql which is bescribed as "MySQL module for php5"

Do I have to enable it in some way?
[/quote]
I use a Suse server. I installed php-mysql the same way as you did and I never had any problem. My issue was on Windows and was a result of the php_mysql library requiring libmysql that could not be loaded.
I did two things that helped me.
1. I put debugging statements in CI to determine EXACTLY where it was failing and I output any information that would help me discover what was happening.
2. I got a utility that told me about the dependencies of libraries. That is how I determined that php_mysql required the other library.

...all the files in my www folder need root privileges, should I change that or simply run ZDE as root as I'm doing now?

In general, you should not leave your files as root. Even if you are the only person using the system. It will require you to login as root too often. If you make a mistake as root, it could be a bad situation. If this site will be a public site, I would definitely not leave the files as root due to security concerns.

PS: the fact that phpMyAdmin runs no problem implies that all the modules are working fine, doesn't it? what's the problem then?

If phpMyAdmin is working and you can use it to access databases, then the problem may be with CI, not the php installation. Consider adding log statements to understand what is happening.