XP Pro ASR restore failure

Customer had Raid 0 System disk(s) with 240 GB total
for the volume.

Total data plus system 57GB. Cust removed one of the
two 120 GB drives due to failure.

Drive capacity now 120 GB but when trying to restore
from DAT backup, using ASR diskette and NTBackup
(SP1)

Boot from Xp Disk and select ASR restore & the
procedure returns with :

“The capacity of the current system disk is insufficint …

“The replacement hard disk must be as large as the
disks present onthe origional system”

How to procede now?