Hi,
I installed Linux first time 2 days ago. CD2 and 3 did not install so I had to first install only KDE and when running, changed source for packages to ftp. After that I can install anything using Mandrake control center.
So I also configured ADSL connection, it workes. If I go to Security section in Madndrake control center, and enable firewall, after reboot I don't have internet. Disabling firewall gives it back.
Help sais that I have to leave firewall open only for services I want outside world to connect to. I don't have any. So now i'm sitting wide open. Any suggestions?

I don't use KDE so I don't know the specifics but there should be some other options aprat from "Turn on/off firewall" to somehow regulate traffic. You should be able to specify which services you want to (un)block. That is probably where your problem lies. I use iptables which is all command-line/script but there are front ends for it like guarddog.

to explain more - under Security tab in Mandrake Control Center, there is checkboxes :
"Which services internet should have access to?":
[ ] - All (no firewall)
[ ] - Web Server
[ ] - ftp server
[ ] - mail server
and some more

by default the first one is selected, others disabled. After I uncheck the All button, others become enabled. As I don't run any servers, I leave them all unchecked. After clicking OK, message appears saying that iptables and shorewall will now be installed. They install ok. After reboot my ADSL connecion will not even connect.

There are other options available uner Security Level tab, which is separate from firewall tab. There I can select many options that I do not really understand, so for now I left them all to default.

Thank you for your time!

It seems that you're right about the checks. If you're not running any servers then you shouldn't enable access to them. However, it may be a good idea to experiment with them just to see what happens (if you haven't already). Same goes for the other options that you don't understand. From what I can see, though, you seem to be rather option-starved. It may be necessary to install a different program (like guarddog) to run your iptables configuration. Once again, I will not be of much help as I don't use guarddog but I've heard good things about it.

Before you go installing too many programs it's probably a good idea (if you haven't already) to read the documentation that comes with the security section of mandrake.

PS: Oh and type at the prompt: iptables -L to see your current iptables rules. This will tell you exactly what rules the security section is setting.