Is it possible to attach an External Alternate "C:" Drive with its own Operating System via USB/IDE cable with its own external power to the main computer system and be able upon startup of the main system to choose which C: Drive to use? If so how would it need to be configured in order for it to work properly? Thank you.

Yes. If your computer's BIOS supports it, you can select to boot from many different devices. Most any computer made since about 1995 will allow either floppy, hard drive, or CD-ROM as the initial boot device. Many newer computers also allow booting from USB and other removeable drives. Some even allow selection from multiple hard drives as to which drive to boot from. Then, there are many sophisticated "boot managers" which will allow just about any boot configuration that can be imagined, regardless of what the computer BIOS supports.

My Bios is able to support USB and I have tried changing it to use USB HDD, but that didnt seem to work as even after disabling the main hard drive in the Bios and requiring a WinXp boot disk it still somehow bypasses the boot order and starts up under the main hard drive anyway. I also receive a message that a High Speed USB Device is trying to use a Non High Speed USB Port and that I need a High Speed USB Host Controller so maybe that is what the problem is and I need a USB 2.0 PCI Card? If I install the USB 2.0 PCI Card in an available PCI Slot will it interfere with the already built in mobo USB Ports that my printer/scanner is hooked up to? What would be a good USB 2.0 PCI Card? The computer does however detect the alternate hard drive as a USB Mass Storage Device though, but wont boot from it...

Before you get too excited on this deal, there are only a few people that can put XP on a usb device with plenty of hassle. Better read up on that before you get your system borked. Trust me on this, not worth the hassle. You'd be better off running a virtual machine under xp even if both vm and host are xp. "Best Practices", Event viewer, host file, perfmon, are in my top 10

I presume that the USB 2.0 PCI Card is in order, I figure that it might be a good idea incase I run into something else that wants it, my only concern on that though is will the USB 2.0 PCI Card interfere with the mobo usb ports that my scanner/printer are hooked up to? Would you mind elaborating on WinXP using a USB Device as it sounds like you have had a bad experience already? Havent had experiences with Virtual Machine, but that sounds interesting?

Mercury There is a good reason why you are asked to supply some system specs. Most computers built within the last 4 or 5 years have at least SOME USB 2.0 ports. When USB 2.0 was first introduced many motherboards had a mix of both kinds. Try a different port. If using a hub it may throttle a 2.0 port to 1.1 speeds. At any rate Microsoft does it's best to prevent WinXP form booting from portable devices. That cuts into profits.

The board that I am using doesnt have USB 2.0 thats why I need the USB 2.0 PCI Card as I tried both ports with the same result.