Windows 2003 server + Oracle, slow

[yuris]

Hello.

I have GP ML-350 with 5 disk RAID5 + 1 Hot Spare
6GB RAM
1 Xeon 3.2 Processor

I have Windows 2003 Server Sp2 + Adapted RAID 2120s Controler
Oracle 10g Version.

My problem is that the Database is very very slow, i have checked the performance monitor, and the avg. Disk queue length is at the top almost all the time.
When the users use the Front Office to write something down on the data base, is taking a very long time, the consulting is a bit more quicker, but not fast enough.

I have already shutdown all the services i didn't needed, i tried to manual insert the Paging files and put "windows choise", but it's still very slow.
I asked my database administrator, but the are also having trouble to speed up the database.

When there is only a few users connected to the database, the system is kind of fast, but when everyone is connected at the same time, it's practically impossible to work.

at first i tough it could be from the network, but if i run the front office locally and try to do something, it is still very very slow, so my guess is, it's not from the network.
This can be only 2 things bad oracle configuration, or something with the server configuration.
Maybe RAID Controller drivers??

What do you guy's think it could be?

Thanks.
Best Regards.