I am not sure this will work, as I have never replaced ntldr, but I have replaced other corrupted or missing files using this method. One way is to insert your Windows XP disk and enter recovery console (i think). Another way (this is what i do) is to download a copy of BartPE and burn it to a cd. It is basically a version of windows that will start off of your cd drive.
Instructions:
1) burn BartPE
2) reboot comp
4) enter the BIOS (usually by constantly pressing Delete or F2 while computer starts), it should tell you briefly what key to press
5) change the boot order (or priority) to cd first. It may require some searching through menus.
6) make sure the cd that you burnt is still in the drive
7) save settings and exit
This thing can't display 8s --->
wait for BartPE to load
9) open up the file manager in BartPE
10) go to the cd drive and into the I386 folder. In here you should find your NTLDR.
11) copy it to your C: drive
12) reboot and quickly remove disk
Then it should work.
I know that this seems like it would take ages, but once you get used to this process it should only take a few minutes to fix problems like this.
