Expanding Raid 5 Array

[nielsen]

I have a Proliant ML110 and am attempting to expand the storage capacity.  Current configuration is:

ML110 G4 Server

Windows Server 2003 SBS

Smart Array P400 controller.  256mb, w/o battery

3 HDs - 146gb 15k SAS drives.

RAID 5. 

This gives me an indicated capacity of 273gb.

I purchased a 4 drive - exact same model as the original 3. 

If I insert this 4th drive it appears as an Unassigned Drive. 

Using ACU, I can create a RAID 0 logical drive using only this one drive.  Or I can add this drive as a Hot Spare to the orignal array of 3.

Nowhere can I Expand or Extend the array - despite the documentation that says I should be able to.

What are my options?  Is there a non-destructive way of proceeding?  Perhaps using the CLI tool?