my macbook has the OS X 10.5.8 version. I was having problems with a wireless network, so I erased the SystemConfiguration folder. After that when I restarted the computer I couldn't access to network preferences and it says airport not configured and no PPPoE configurations were found.

I restored the ereased files but It is still the same.. and I have just noticed that it says there is no bluetooth device and a baterry either... I don't know what to do? I am in europe studying and I left my installation discs in america..

Sorry - the best thing to do is reinstall using the Archive and Install option.

If that SystemConfiguration folder was in the /Library/Preferences folder, then a restart should have simply reset the system configuration - mostly your network settings - to defaults, and you would simply set up your network again. That folder has a few primary .plists for your system networking. It rebuilds itself when you restart, and then setup your various connections. That must have been what you meant to remove. I suspect you may have removed a different SystemConfiguration folder, inside your /System/Library folder
That, unfortunately would basically disable your system networking, and some other hardware accessories, such as bluetooth, and other networking _bundles_
Not a good misstep, if you don't have access to an installer.
If you have brought a backup drive with you, then you can get that folder from your back up. If not - then you will need to find an installer. If you are in a large city, or close to one, you may be able to get some help at an Apple store.

First try to Reset Your PRAM (http://support.apple.com/kb/HT1379) to see if that helps.