I recently installed Ubuntu 12.04 into my system on a separate partition. However after the installation was successfully completed, the system keeps booting Windows XP without showing the dual boot screen. Any suggestions, please?
Welcome to Ask Ubuntu! This is a rather common question, people install Ubuntu alongside Windows, but Windows still boots without offering the option of Ubuntu. This is often caused by GRUB/GRUB2 (the bootloader that allows you to choose which OS to load) not being installed in the Master Boot Record (the place that tells the BIOS what to boot).
The fix usually is pretty simple, there are two relatively easy options (taken from https://help.ubuntu.com/community/Boot-Repair
Then, once it's installed, do the following:
Hope this helps!