error after moving glpi from windows to linux

Hi I'm a newbie here,

I have installed GLPI (GLPI 0.71.5) on a windows 2003 server. This server is installed with Mysql 5.x en PHP4> i suppose
It works fine but the server is instable.

I also have a shared server which is a Linux (Debian 3.x) host. with mysql 5.x and php5
They've installed parralels with plesk etc... nice environment.

I copied the whole folder in which glpi resided on my windows server and copied this folder and subfolders to the linux server.
With phpmyadmin I first exported the database from the windows server and imported the database to the linux server.

This is what I did with all my PHP/Joomla websites. That works fine.
In some cases i had to change some paths because the regular windows paths doesn't seem the same as linux.

But GLPI is different. I see something on the screen after I start GLPI.
But the following errors came up :

-A link to the Mysql server could not be established. Please Check your configuration

-Warning: Unknown: open(./files/_sessions/sess_bcc3b328b4e8b0ec9d5b2dcc124ac4e6, O_RDWR) failed: No such file or directory (2) in Unknown on line 0

-Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (./files/_sessions) in Unknown on line 0

Does somebody knows what the problem is?
I can't find any config files within GLPI to set some path's which in Joomla you can do in configuration.php for example.
Is the way I installed GLPI the right way to migrate from windows to linux?
What is the appropiate way to get this work?
Is it possible to install a new version on the linux server with the old database?

I'm not an expert in This please help me.

John de Haas