Boot doesn't display Windows XP and Ubuntu to select the OS

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http://askubuntu.com – I recently installed Ubuntu 12.10 as dual boot to my Windows XP. There was a booting problem: NTLDR is missing. I resolved by adding two system files by copying two files by using Windows XP bootable CD. Now, I am not able to get Select OS screen as before. Directly Windows XP is being started. So, I re-installed Ubuntu but still cannot get the OS selection menu. How can I resolve this problem? (HowTos)