According to your initial post, I assume that you've got a used hard disk and want to install it on your own PC. I also assume that he is not gonna want the hard disk back, since he's getting a new PC and is also heading out of town. In that case, what you need to do is to set the jumpers on the back of your hard to either CS/Master and the one on your friend's to CS/Slave, and then connect the hard disk to your computer as a Slave. So when you restart the computer, what will happen is this:
Your C:, drivers and all programs installed on C: will remain intact. There will be no need to reinstall or uninstall anything.
The new hard disk will not conflict or ask you to boot into Windows 2000 Pro or anything like that, your normal Windows OS (9x/Me/NT/2000/XP/2003) will continue to work the way it always has been working.
Once its booted in, you can format the hard disk and delete/change partitions any which way you want. Drivers/applications on your hard disk will remain and work the way they used to and no drivers/applications on your friend's hard disk with conflict with anything on your PC.
However, there is one problem that can arise if you're not using Windows 2000/XP/2003 as "your" OS. Your friend's C: will become your D:, and if you have a D: on "your" hard disk, then it will be auto-renamed to E: Which means, that any applications you've installed on D: will not work properly and you will have to use a program called "TweakUI" to detect and fix the changed drive letters/directories.
If you're using Windows 2000/XP/2003, then it automatically add the disks to the end of your first hard disk, so if you have C:, D: and E: your friend's HDD will be F:, G: and H:, etc.
If you do not want to use your HDD at all, and want to use ONLY your friend's then ignore all these steps and then connect your friend's HDD and then start the computer using a bootable startup disc/bootable CDROM and then use the 'format' command to wipe the hard disk contents. You cannot start the computer by plugging in your friend's hard disk alone as a Master.
Hope that clears things up.