Just want to throw this out there. To date I've not heard of any issues whatsoever with dual-booting Windows 7 and XP, but I've found a situation that just doesn't work.
The older ICH5R/82801ER controller is part of the i875P chipset that is the basis to our standard workstation at work, and was the chipset the Abit IC7 that is in my general system at home (it was my game system 2 generations ago) is based upon.
And it will not, will not, dual boot XP and Windows 7 on the IC7 motherboard. I've mucked about with it for almost 2 weeks, including breaking the the mirrored RAID array and moving the XP installation to standalone non-mirrored drive, and regardless, after Windows 7 is installed the XP installation blue screens upon boot. The XP installation is bootable in safe mode, but normal Windows mode is a no go - and no amount of working with it fixes it, excluding the "full wipe of the drive and reimage the original partitions back onto it" that is sometime required to fix faulty RAID metadata with this controller.
This controller has given me grief in the past because the BIOS and driver both are easily confused if anything unexpected is found in the RAID metadata area, and I'm presuming that the Windows 7 installation is putting something there that the XP driver isn't kosher with (even though they both are using the same driver version), but the bottom line is if you plan to dual boot the older controllers that support RAID, A few extra precautions to preserve your installation might be well worth taking - just in case.
What I did not try was installing Windows 7 to a different drive in the same system. This is because instead of doing that, I'd disconnect the XP drive, install Win 7 to it's own drive, and then reconnect the older XP drive and switch the boot drive in BIOS to control which OS to boot.
But since the 82801ER only supports 2 drives and I don't want to give up the ability to periodically mirror the drive to a backup drive, I'll probably just forego Windows 7 until such time as the XP installation needs rebuilt or some other reason comes up.
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