It is necessary to first create the disk that Windows will see and use (creating a RAID array). This is really the only fundamental difference between installing XP on this server and installing XP on current/semi-current hardware. Loading drivers for the storage controllers is not a new thing either. XP is so old that it doesn't know how to handle SATA drives, so loading the chipset/AHCI drivers (the device handling drives connected to the motherboard) is also required for all XP installs. The two major exceptions to this are: 1) installing XP with the onboard SATA set to ATA/IDE/compatible/legacy (a bad idea and a cheap shortcut), and 2) installing XP SP3, which added a few of the most common chipset/AHCI drivers to the installation files. Unfortunately, many people simply disable AHCI in the BIOS to get around loading the proper drivers for their system during the install.
Use nlite to integrate the RAID drivers (and SP's if your XP CD doesn't have at least SP2), then simply boot to the XP CD, and install (you will have the option to create any specially-sized partitions that might be necessary from there, including formatting the disk (full or quick) as NTFS (recommended) or FAT32).
Let us know how it goes.