It isn’t Windows7’s fault that you were dualbooting 2 OS’s off the same HD and then ran an unknown cleanup program from inside the lesser OS.
Take all HDs out except the one that had XP/Win7. Boot to the Windows7 install DVD and at the main screen hit Next, then Repair your computer. The installer will then scan for windows installations. When it’s done scanning hit Next then use the Startup Repair tool. It should scan for problems, like a missing BCD, and either repair the existing one or create a new one if it’s missing or corrupt.
NTLDR should be missing because Windows7 takes over the entire boot process and since it doesn’t need the WinXP boot files it removes them to prevent the computer from accidentally using the WinXP boot manager instead of the Windows7 BCD. Depending on how much of the WindowsXP and Windows7 installations were corrupted you may end up having to reinstall both OS’s.