Problem with 2 operating systems on the same hard drive on dell inspiron 1501

So i have a dell inspiron 1501 with Windows xp pro x64 SP2 on it and well i tried to up grade it to SP3. so i burned SP3 to a DVD and every thing was going well until it wasnt i had burned the wrong ISO image and it was a full installation of windows xp. so i stopped the installation but now when ever i boot up the pc it brings up a choice of windows xp pro x64 which is the one i want and windows xp pro. and if you don't select one within 3 seconds of the screen appearing it automatically choses windows xp pro and tryes to install it. so i want to know how to delete the installation file for windows xp pro and keep just windows xp pro x64 as the operating system. i normally am a tech guy and now ALOT about computers and coding but i just cant figure this one out. please help this is not urgent that i fix this but its really annoying and makes the computer boot up way slower than it normally does