Step 4 - Edit boot.ini:
In Vista, the boot.ini is not editable directly, as the file itself is hard to locate, so we will be modifying it through "Boot
Configuration Data Store Editor" bcdedit.exe:
(Just as an explanation, the loader type for XP is an NT Loader, hence the use of ntldr)
-first open a command prompt with administrative privilages (right-click and choose "run as administrator")
*Note the following 2 answers from bcdedit for each item are acceptable:
"The Operation Completed Successfully"
"The Specified Entry Already Exists"
Be sure to type each line carefully (replace C in the first line with the drive containing your Vista installation):
bcdedit –set {ntldr} device partition=C:
bcdedit –set {ntldr} path \ntldr
bcdedit –displayorder {ntldr} –addlast
bcdedit -set {ntldr} description "Microsoft Windows XP"
The completed bcdedit file should resemble this:
-This will correctly add XP to your boot sequence, and even name it properly instead of "Earlier Version of Windows"
-the displayorder line also allows the entry to be visible under the advanced settings of your computer properties.
Vista is the default boot, if you wish to change this to XP it can be done by setting {current} to addlast, or under the computer
-> properties -> advanced settings.
If all done properly, XP and Vista will dual boot properly!
boot.ini edit 
