There is no need to set the boot sequence to Floppy first, since you really need to boot to from the CD first, you are never booting from a floppy with a normal XP install (unless the system doesn't support CD booting, and in that case you probably don't want XP on it since it is so old).

Now as to the SCSI being the 3rd device in the boot sequence, that would only be true if the BIOS on the motherboard was setup to recognize the SATA as SCSI, it has nothing at all to do with WinXP's recognition. Win XP install could care less what the boot sequence is set to, and has no way of knowing what it is set to, you really only need CD first to install it, then the sequence needs to be set so that that SATA drive is booted after the CD

You could also load the driver from CD at the point after you hit F6, when it asks for the driver for the natively unsupported device. This is something that people setting up servers with Raid arrays or unusual SCSI configurations have had to live with for years.