Thought I'd already posted this question today but it seems to have disappeared. Had two 80Gb SATA drives in 'striped' mode. The one with the O/S failed. I installed XP+SP2 on the remaining drive after deleting the RAID configuration, everything ok. New replacement drive turned up today but is 160Gb (how generous of Maxtor) I fitted the drive and set RAID to JBOD. Both drives recognised in RAID but not in BIOS or Windows, I assume because the new drive is not partitioned or formatted. FDisk won't see the drive. Can't use Maxtor Maxblast because the VIA chipset is not supported. My mobo is ASUS K8V-X SE. Windows only sees C: drive as 80Gb.
Disk Management is built into Windows XP so it is there. Big Elf just missed one step from his post and he should have said Control Panel, Administrative Tools, Computer Management, Disk Management. Alternatively right-click My Computer and choose Manage from the menu then Disk Management is near the bottom on the left. Click on it and all installed drives appear on the right. Right-click the drive to partition it and format. Your drive will not appear in My Computer until you have done this.