The Vostro 200 uses an Intel ICH9 controller. As mentioned in Asianux Server 3 SP1 and SP2 release notes, you need to set the SATA mode to RAID in the BIOS.

Turn on your machine.
Access the BIOS: press F2.
Set the SATA mode to RAID:

Integrated Peripherals -> SATA Mode -> RAID
 
Save and reboot.
Install Asianux Server 3 SP1 or Asianux Server 3 SP2.