Please read this thread, stickied in the Operating Systems category.
Windows XP Professional x64 Edition: Drivers, Free Trials, and Availability. I would not recommend installing the 64bit version since drivers are not yet prepared for the hardware, which makes the operating system very beta test quality since you will spend much of your time figuring out how to get the darn system to work, only to be unsuccessful in the end. If you really want 64bit processing power, install Ubuntu Linux. That 64bit system is probably better prepared for the casual user than Windows XP 64bit is.
Please, read through Mechbgon's PC build guide.
Photo guide for 1st-time builders
To install raid 0, I suggest following the instructions in your motherboard manual.
To copy files over, you can install your old IDE drive in your case on the IDE ribbon cable but make sure not to boot from it. What you can do is select "none" in the bios for the Master IDE drive so the bios does not attempt to boot the system from your old drive. You can manually copy files from your old drive to your new system. You may be able to use WinXP's settings transfer wizard, I have never used this so cannot help more with this. Local email files and HTML bookmarks are files you will want to export before dissassembly of your old system. Also, such settings as MSN Messenger, Skype, and others may need to be exported. Consider each of your installed programs to see if it contains data you will want to bring with you to the new system.
Your hard drive manufacturer probably has a diagnostic utility that includes the option of copying the data from your old drive to your new drive. Doing this may remove the necessity of installing a new system, if that sounds like something you wish to do.