It sounds like a Dell-branded LSI MedaRaid 520 U320 card. Unfortunately, Dell is notorious for taking the retail version of server cards and crippling them with custom firmware and modified drivers, and only work on supported Dell servers. Flashing the retail firmware on them won't help, either.
Not a great idea, but usually the Server 2003 (non-storport) driver will work fine on Windows XP. Does the Dell driver for the server have this driver?