First make sure you know which one is the one that works, and whether it is the default one (the one which is highlighted on the boot menu is the default one - which is not necessarily the first one on the list).
There is little risk in what you need to do, but since the two boot choices have the same description, back up your boot files first. Go into XP, My Computer, C drive. Click Tools, Folder Options, View tab. (1) tick "Show hidden files and folders" (2) Untick "Hide file extensions for known file types" (3)Untick "Hide protected operating system
files". click OK.
Back on C drive, you should see three files ntldr, ntdetect.com and boot.ini
Insert a floppy. Right click drive A and select format. On the next screen click Start and do not tick any of the options. You must do the formatting, even with a new floppy, and you must do it in XP. After formatting, copy the 3 files mentioned above to the floppy.
You can use this floppy to boot into XP. Remove floppy.
Then right click My Computer, select Properties, select the Advanced tab. Startup and Recovery Settings.
Under System startup, default operating system - click the drop-down list, and make sure that the right one is selected. Since they have the same name, be careful. If the first one on the list is the one that works, select the first one on the list (if not already selected). click OK.
Go back to Startup and Recovery, click the Edit button. The boot.ini file will open in Notepad.
On the assumption that you have selected the right default OS previously, the only thing you need to do is to delete one line.
Under the section [operating systems] in the boot.ini file, delete the one which is not working. The order corresponds to the boot menu you see on startup.
So if the second one is the one that doesn't work, delete the second line, i.e. multi(0)disk(0)rdisk(0)partition....="Microsoft..." /fastdetect.
Save the changes and exit. Click OK in Startup and Recovery. Restart.
Just in case you have deleted the wrong line and you can't boot into Windows from the hard disk, use the floppy to boot up the computer, you will get the same old boot menu, and go back into the working XP.
If the editing works correctly, you can either forget about the backup floppy, or better yet, copy the new boot.ini fle to the floppy, replacing the old one, as a backup of your boot files.