If you are having issues getting windows XP installed with a raid, be sure that you have first already copied the raid drivers over to a floppy disk. It shouldn't make a difference whether the floppy is and external or internal drive. Once you have the information on the floppy disk, make sure that RAID is set up in the bios and you array is set as well. Once the read is set boot from the Windows XP install CD.

Once the OS is asking you to select the driver from the floppy, you will have to install ALL of the files on the floppy. Starting from the bottom, work your way up 1 at a time and keep selecting to load another driver as the ICH controller on the P55 chipset requires multiple drivers. Be sure to track where you left off as the list will constantly start you at the bottom.

Once all the drivers on the list have been selected proceed with the install and you should no longer receive the STOP message.
Please note this is only an issue with Windows XP and is prevolent with both 32 and 64bit.