Just to let you know things look a bit more promising on further investigation. I let the server boot off the HDD and was greeted by NT server (a surprise - this box was supposed to be wiped). Once I got around to mounting the 'partitions' I'd previously assumed to be individual disks using the LiveCD, I realised that they actually were partitions: sda1 holding the Dell configuration tools (executables and floppy images); sda2 containing Win NT; and sda3 the large, blank partition.

The Dell/Adaptec PERC/2i card is (appears to be) supported by the aacraid kernel driver (an Adaptec/Red Hat joint effort). I want to find out more about the driver before installing anything on the array, but it seems that other people on various forums have made it work...