This particular problem is noticed when you have installed Microsoft Windows Vista BetaRC1 on your existing Windows system, in dual-boot mode. While installing windows, Vista overwrites the system MBR (Master Boot Record) and gives you an option between Windows Vista and Windows XP or any other operating system. When windows Vista is uninstalled, one expects, not to see the dual-boot menu, but this isn't quite the case. There could be three possible solutions for this particular problem as discussed below in detail below.

Solution 1:

The Boot Configuration Data (BCD) store contains the boot configuration parameters which controls the start of Microsoft Windows Vista and Microsoft Windows Server Code Name "Longhorn" operating systems. Previously these parameters used to be in the Boot.ini file (in BIOS-based operating systems) or in the nonvolatile RAM (NVRAM) entries (in Extensible Firmware Interface-based operating systems).

Bcdedit.exe, located in the WindowsSystem32 directory of the Windows Vista partition can be used as the command-line tool to alter the Windows® code which is run in the pre-operating system environment by adding, deleting, editing, and appending entries in the BCD store
Why was there a change to BCD from Boot.ini?

Improved mechanism for describing boot configuration data was the main intention for changing to BCD from Boot.ini. With the development of new firmware models (for example, the Extensible Firmware Interface (EFI)), an extensible and inter operable interface was required to abstract the underlying firmware.

This new design provides the foundation for a variety of new features in Windows Vista (for example, the Startup Repair tool and Multi-User Install shortcuts).

VistaBootPRO is an application, which is used to make changes to the Windows Vista Boot Configuration Data (BCD) registry quickly and easily.

Designed for both beginners and advanced users, VistaBootPRO can be used to make "cosmetic" changes to the Windows Vista boot Menu, such as changing the name of the Operating Systems shown in the boot menu and also can be used for more advanced "functional" changes like adding an Operating System to the boot menu and repairing the Windows Vista boot configuration data.

Advanced settings include backing up and exporting the boot loader configuration, and modifying various details for the entries.

For those who have used bcdedit.exe in the past, you will be impressed with the ease of use and functionality that VistaBootPRO provides.

Install this software on your Windows XP system and delete the Windows Vista entry. It is advisable to make a backup of existing boot config using VistaBoot Pro incase anything goes bad.

Solution 2:

This solution is the second best option for the problem. To achieve this you'll need a Windows XP Home or Windows XP Professional CD.

Make necessary changes in the BIOS settings, so as to boot from CDDVD-ROM drive and boot from your Windows XP CD. Now, you would see screen as below, Choose the "Recovery Console" option by pressing 'R' key.

Now it should display the screen below as shown below, if asked enter you Admin password:

Now, type FIXMBR and press enter, press 'Y' to confirm as shown below:

Now, you need to type: FIXBOOT and press “enter”, press 'Y' to confirm

Now, remove the XP CD from drive and restart your computer, and this should remove the EXTRA Windows Vista Boot Option.