|There's no such thing as "XP driives".|
Windows 7 will recognize the FAT, FAT32, or NTFS partitions and the data on them fine.
If you mean they each have a Windows XP installation on them.....
- you can't load an existing 2000 or up Windows installation if the hard drive is not internally connected to the computer
- if the hardware (primarily the chips on the mboard) of the Windows 7 system mboard is more than a little different from the mboard that was present when XP was installed on the hard drive, shortly after the initial graphics appear for XP, one of several possible things will happen, and XP WILL NOT LOAD all the way.
That can be fixed but that requires you have a suitable XP CD, a suitable Product Key for it, and that you run a Repair installation (of XP) procedure, if you do not want to lose the personal data you have added to the partition Windows was installed on .
- you can set Windows 7's multiboot feature so that you have more than one operating system to choose from when you boot, HOWEVER, EVERY TIME you boot from an XP installation, the System Restore restore points will ALL be deleted in Windows 7 !! (The same applies to Vista)
If that concerns you, you must use
- the Bit Locker feature of Windows 7, but that's only available if you have the Ultimate, Professional, or Business ? version of Windows 7
- or - a third party boot manager program that can HIDE the partition Windows 7 itself is installed on from XP detecting it while booting XP.
E.g. I use BootIt! N.G. for dual booting XP and Vista, but it's not free,