If you have done a reformat of your hard drive and proceeded to do a successful Windows XP installation, you may notice that a choice between two operating systems when you start up the machine.
Here is how to get rid of this:
At the top of the System Configuration Utility, choose Boot.ini
Next, click on "Check All Boot Paths"
Once you do that, a box will come up saying something is invalid and asks you if you would like to remove the invalid one.
Choose to remove it
Restart the machine...
Now, you will notice that you do not get prompted to choose an operating system.
Once Windows boots up, the system configuration utility window will come up. Put a check in the box, and press ok.
That's all there is to it!
Why does this happen? Well, it's because of the Master Boot Record or MBR.
The Master Boot Record is the very first sector of your hard drive. This sector has all of the boot information. In other words, the MBR tells the computer how to boot. Keep in mind, the Master Boot Record is in no way part of the main partition of the system. So, when you do a complete reformat of your hard drive, whether you use NTFS or FAT32, you are not actually formatting the Master Boot Record. So, since the Master Boot Record held information from a previous installation of Windows, it is telling the computer that the Operating System still exists when in fact it does not.
I should add that this only works for Windows XP Professional. If you are using Windows XP Home Edition I suggest you do not attempt to edit the Boot.ini file yourself, because you can crash your system.