You need to modify the boot.ini files in Windows
This file is located in the
root directory of the primary drive.
How to modify the boot.ini:
The boot.ini file is a hidden system file located in the root directory of your primary hard disk drive. To edit this file we recommend you follow the below steps.
1. From Windows, open an MS-DOS prompt by clicking "Start" and then "Run" and typing "cmd" in the text box. If you are not able to get into a MS-DOS prompt to edit the boot.ini file, boot into the recovery console to edit the file.
2. At the MS-DOS prompt, type:
c: <press enter>
cd\ <press enter>
attrib -r -a -s -h boot.ini <press enter>
edit boot.ini <press enter>
Delete the Windows Vista Option there
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Right click on My Computer, and select Properties. Now click on the Advanced tab. In a section labeled Startup and Recovery click on the button labeled Settings. You should now be looking at a dialog like this:
Startup and Recovery options
Click on Edit to edit the startup options file (aka boot.ini) manually. That should open Notepad with something similar to the following from my machine:
[boot loader]
timeout=5
default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /NoExecute=OptOut
C:\CMDCONS\BOOTSECT.DAT="Microsoft Windows Recovery Console" /cmdcons
In this example, you can see that I have two options to choose from when I boot: Windows XP, and the Recovery Console. I'm guessing you have an additional line for the XP Pro Setup that you had trouble with it. You can simply delete that line.
And if you're tired of having the computer wait 30 seconds for you to choose an operating system, you can also change the timeout value, as I have in my example.
Save that file, and when you next reboot you should no longer have that additional option.