In Windows XP if you want to modify the bootloader, just right-click on My Computer, select Properties, go to the Advanced Tab, and click Settings under Startup and Recovery, then click Edit. This opens a local file – boot.ini. It’s just a standard text file and you can change pretty much anything. Unfortunately it’s not that easy in Vista – you can still navigate to the Startup and Recovery settings, but all you can do is select which operating system is the default and modify the timeout settings.
To edit Vista’s boot manager you have to use the command line BCDEDIT utility. To access BCDEDIT, run the Command Window as an administrator and type in BCDEDIT.
Unfortunately BCDEDIT isn’t an easy tool to come to terms with, especially as it’s purely command line-driven. So, a great tool to use here is EasyBCD by NeoSmart Technologies. EasyBCD offers a GUI frontend to BCDEDIT, and makes life much easier.
EasyBCD 1.7
http://neosmart.net/dl.php?id=1
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Windows Vista no longer starts after you install an earlier version of the Windows operating system in a dual-boot configuration
http://support.microsoft.com/kb/919529