2nd Hard Drive with XP

Skip to point 6 below to ensure your BIOS supports a convenient way of booting from multiple hard drives. If it does not then I wouldn't bother.

The simplest and safest way to do what you want without any complications is:

1. Disconnect your current drive that is the home of Windows Vista.
2. Connect the second drive as the only drive in the system.
3. Install Windows XP as if it were the only OS in the machine (since the other drive is disconnected at this time, the Windows XP installation will in fact be the only OS in the machine, though temporarily).
4. Configure XP as needed e.g drivers, programs, and whatever else you want.
5. Reconnect your original primary drive (the one with Windows Vista)
6. As long as the motherboard you've got gives you a boot menu facility, you will be able to boot from either drive. If the motherboard does not offer a boot menu facility, then it - hopefully - gives you the option to select which drive to boot from in the "boot" section of the BIOS. If neither of those options are available to you (some cheap boards don't allow you to specify which hard drive to boot from) then it is a hassle, you'll have to physically swap the connections between the drives to switch which one becomes the boot drive (too much hassle IMHO).

HTH.

Most operating systems allow for 2 different os's to be installed and use a boot menu to select which one you want to boot into. I have Vista and Windows 7 installed and can select which OS I want to boot from with the menu. Windows XP will allow you to pick the HD you want to install to and then it should also see the other OS installed and give you a boot menu. You can also go into Windows and select which OS you want to be the default boot OS.

You are correct but, that works when both OSs are installed on the SAME drive.

If the OSs you want to choose from are installed on different physical drives - which is his case - then BIOS support is need to first select _which_ drive to boot from and then, which installation from the selected drive (which is done by the Windows boot loader as you explained).

ASUS, Gigabyte and a lot of other manufacturers have a boot menu option at startup to select which drive/device to boot from. Cheaper motherboard models tend to omit this feature however.

HTH

^ Yeah, I did the dual boot thing for a while with XP and Vista on different drives.
You add both drives as bootable, and then there is another option you can set that brings up a menu during boot for you to select which OS you want to boot to.
After a while, I just got tired of it, decided there was really no advantage to having 2 OS's, so you know what I did? I formatted the drive with Vista and went back to using XP.
I am not saying there is anything wrong with Vista, I just can't figure out why so many think they need it!
64 bit Vista is nice if you need a lot of RAM. But there are very, very few people who actually need more than 4 gig of RAM. And the catch is, the only real reason to have more 4 gig for most users, is because they are running Vista!
32 bit Vista is.....well, you might as well have stuck with XP.
Oh yeah, DX10, I forgot about that. Well, when I was running Vista 64, DX10 did not impress me all that much. Could not tell much, if any difference over DX9 with all the eye candy turned up. Well, no difference except that it ran a lot slower.......