BleepingComputer.com: Dual boot between Vista and XP, help !!!

Hi, pls help me to solve my problem.
The thing is I installed Wins Vista to Primary Disk C: (first), and then I installed Wins XP to D: (both Wins on the same HD). I made my bootloader for both of them work great.
However, now, after I format my C: (Wins Vista) and reinstall it, I can't boot to XP. It alwasy say missing NTLDR file even though I tried to back it up, but It still doesn't work.
Pls help me to solve it, thanks so much.