It is an easy thing to do once you copy all of your files that you want to keep to the second drive (don't forget files on your desktop and your e-mail database file etc).
when your ready just boot your PC from the windows CD-ROM.
Select install windows (not repair).
Click through the screens till you get to the screen to select where to install. select the C: drive and select delete. then select the (now) free space and select create partition. then select install..
When prompted, select format NTFS (not quick format)
If your going to do this then i would recommend that you surf the net and make sure that you have a copy on your second disk drive of all of the latest driver install files for your system (inc video card, sound card, motherboard drivers, etc) as well as any common apps and utils that you use (like a firewall (
www.zonealarm.com is free), anit-virus software, acrobat reader, winzip, etc) so that you can compleat the install and secure your PC before you risk going to the web.
Hope that helps.