Is your BIOS up to date?
With the SATA RAID/AHCI option, there should be a SATA Port0-3 Native Mode option that should be enabled as you have XP. My experience is that having an AHCI SATA non RAID system does involve a slightly prolonged startup.
However, have you looked for a fast boot option in your BIOS and checked if you have /fastdetect in your boot.ini file? If this means nothing to you - TAKE EXTREME CARE, mucking up the boot.ini file will stop your PC from starting properly, if at all.
You can look at/change boot.ini via start - run and typing 'msconfig', where you can also see what programs are begun on startup and disable those not required at startup. Again, best steer clear of msconfig until you've done some homework.
You can also look and edit your boot.ini by
1. right clicking on my computer and selecting properties
2. select 'advanced' and then 'startup and recovery'
BUT be careful, if in any doubt, don't change anything. The more experienced members of the forum will no doubt have other, hopefully simpler solutions. Good luck.