The solution finaly was simple...
A Hosteurope coworker told me that they think it is normal to do not install a Kernel wich supports quotas...
The real problem, I think is the special Hardware from Dell, wich need a couple of special drivers.
They told me that the change of the Kernel, wich I can't do by myself because of the Dell drivers I could not find (they are only available for Dell customers, I think), will produce costs. After some phonecalls they do it without computation...
Now everything works and my opinion about Dell is still the same...
Thanks everybody for the Help