first of all, is the error nltdr.dll or ntldr.dll?
if it's ntldr.dll, that file is VERY important, and usually means the HDD is failing. Try reformatting, and running a scan for bad sectors.
If the hdd is teh master, change it to slave, and make sure the jumper configs are right.
also try downloading this: http://www.windows-error-repair.com/download.php?t=23