Buy the adapter as locs4dayz above me suggested. It's cheaper to buy the power adapter (4pin molex to serial ATA) than it is to get a new power supply.
If you are installing Windows XP you will need the manufacturer's driver for your specific motherboard RAID chipset; aka
SATA DRIVERS.
There are other options as a work around, one of them is to install Windows Vista and not worry about those drivers because the DVD already has them preloaded.
Don't fret, you can slipstream said SATA drivers using NLite onto a revised Windows XP installation CD. With XP, you are required to have a floppy drive on hand to install SATA hard disk drivers prior to the actual WindowsXP installation.
Slipstreaming is a way of integrating these specific drivers together into the installation so that you don't need to buy a floppy drive. However, if you do have a floppy drive, boot from the XP CD, and Press F6 to install the SATA (.inf driver file) that you just downloaded to a floppy disk, and proceed with the on screen instructions.
Nlite download- program used to integrate your drivers onto a REVISED XP installation CD.
http://www.nliteos.com/download.html
Slipstream instruction guide:
http://www.nliteos.com/guide/part1.html
Also, as an alternative, if your new motherboard has both of the SATA and IDE interface connectors. Install a fresh copy of Windows XP on to the old IDE drive, followed by the SATA drivers, and then install Western Digital's DataLife hard drive software.
After you're done with that, Plug in the new SATA hard drive and transfer XP to it using the DataLife program. Then disconnect the IDE drive, and upon reboot, change your target boot device to the SATA hard disk and you're set!
Download the Windows version of DataLife here:
http://support.wdc.com/product/download.asp?groupid=612&sid=3〈=en