Hi Shard,
No, I mean the "Xserve G5 PCI Hardware RAID Card" card.
You can find it on the Apple Store - it's the first item under "Server Accessories".
Here is the description:
"This 64-bit/66 MHz PCI card provides enhanced reliability and performance to Xserve G5's internal Serial ATA (SATA) drives using a hardware RAID controller. Bypassing the on-board hard drive controllers, this card provides three independent 150MBps Serial ATA controllers backed by a high-performance RAID processor and 64MB of RAID controller cache with an on-card backup battery."