If you want to run Windows XP on your old, but once both expensive and shiny, server you have a problem with your RAID sets: Dell won't provide PERC4/SC drivers for the consumer operating systems, and using Server 2003/2000 drivers doesn't work on XP. You are now in quite a pickle.
Dell has historically made a lot of RAID controllers of various kinds. Which of course means that Dell really make nothing at all; they make OEM deals with different manufacturers. The OEM suppliers have typically been LSI and Adaptec, and Dell call these adapters PERC and CERC regardless of manufacturer. PERC are the fancy-schmanzy SCSI and SAS adapters, while CERC are ATA/SATA only. The number after PERC denotes the "generation", in this case, the fourth. These adapters are not well known for their performance, but they are pretty solid choices for stability, and you can get support and spares for quite some time. Many of these adapters have a counterpart in the OEM manufacturers own lineup, but some, such as the CERC SATA 1.5/6ch, have no direct OEM cousin -- Adaptec's offerings for that adapter being four- and eight-channel instead.
The Dell PERC4/SC which is a middle-of-the-road SCSI RAID adapter capable of up to RAID5, and which can be optionally outfitted with a backup battery for the 64MB cache, is really a LSI MegaRaid 320-1 controller in disguise. If you already run the latest Dell firmware, you can just download the LSI driver and install it (as of writing this, it is version 6.51.32). This can also be used as the "F6 boot disk" in Windows XP. Just select the "MegaRAID SCSI 320-1 RAID Controller" from the list. Windows won't complain.
I read on them interwebs that you can upgrade the firmware from Dell to LSI, too, which you might do if you are very very brave; however, I am going to go and recommend against it, because frying your expensive adapter is a very sad event indeed.
Edit: I upgraded the firmware to 1L51 because I am very very brave. No ill effects, but 44% better performance! Average went from 36 to 52 MB/sec in a RAID5 array, which is still pitiful considering this is four 10k drives. Don't upgrade, and if you do, nothing that happens is my fault and I don't want to hear about it. Hugs and kisses.