1st you will need to boot from your Windows CD into the recovery console.
Here are the instructions.
http://www.microsoft.com/resources/d....mspx?mfr=true
When you get to the c:\ prompt you need to type chkdsk /r and enter.
This will take a long time on a large hard drive.
After this finishes, type fixboot and enter. This one is quick.
Now type exit and enter and your computer will reboot. It should boot into Windows now.
Let us know how it goes.