Did you install Vista with XP drive installed and plugged into motherboard?
If yes, then use Vista boot Pro. Install it in XP. (you won't need it after
you install the Vista boot). IF NO, then you need to choose your boot
options in your bios.
Why?
Chances are you're here because you're running Windows Vista and want to do
one of two things. Install a second OS or manage your boot configuration
without directly editing the BCDEdit file. As you likely now realize,
Windows Vista has made this task somewhat complicated for most users.
VistaBootPRO was developed to make changes to the Windows Vista Boot
Configuration Data (BCD) registry quickly and easily, doing the job in a
fraction of the time it would take using the alternative. The only other way
to edit the BCD is to use the command prompt application "credit.exe,"
located in the Windows\system32 folder of Windows Vista, which requires
users to become familiar with the ins and outs of the credit.exe switches
and options, leaving many frustrated users in its path. VistaBootPRO allows
users to easily and neatly organize their boot configuration entries from
within all flavors of Windows.
Once installed, choose Manage BCD OS Entries. If you do not see Vista in the
large window, then you do not have a boot loader set for it. In that case
select "Add New OS entry" Type the OS name (Vista) then select the type
(Vista) and then the boot letter in your case it's E. The click apply
updates. You should now have 2 OS boot options.
Get Vista Boot pro from
http://www.vistabootpro.org/.