Remove Dual Boot
 

-right click on my computer, select properties
-move to the advanced tab
-under 'startup and recovery' select settings
-in the new dialog box you have a couple of options:
-if you wish to leave DOS on the machine, but not see the option screen you can simply set the 'time to display list of operating systems:' to 0 as winXP should now be ur default OS
-if the removal of dos is your goal, then click edit
-first save a copy of the notepad file which opens 'boot.ini' just incase you make a mistake
-now there will be a lines similar to:

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOW S
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Micro soft Windows XP Professional" /fastdetect /NoExecute=OptIn

*There will also be a line for dos here under [operating systems] something like 'multi(1)disk(0)partition(#).....'
-check that your default line points to XP, as it does above
-now erase the line with the other OS, in this case DOS 7.1 ie. 'multi(1)' NOTE *the entire line may be more than one line in notepad*
-save the file
-then you are free to erase the folder associated with the erased OS NOTE *if a mistake was made, you may wish to do this as the last step*
-reboot your system and its done.

-upon any mistakes load into either DOS or XP, etc which ever is easiest (or still remaining on your system)
-copy the old boot.ini over the modified one, and try again
-good luck