Try this at the start-up (the one when you cut it on at the black boot screen choose xp and go to the c: drive (my computer) look in your files for the ubuntu 8.10 folder or linux folder and just delete it it might still be an option on the boot screen but it will be gone off your hard drive and if the ubuntu has made it self your main system i hope you have a windows os disk if you don't i hope you have another computer and get the hard drive out of it and make it your master drive(main hard drive)(follow diagram on the hard drive sticker most hard drives have one) and make the one you want to fix the slave(secondary hard drive) and just do as first described look for the ubuntu folder and delete then put your computers back like you had them before you forget which hard drive is which! I hope this helps you get your computer back like you wanted it have a nice day! Over and out! DO NOT EVER FORGET THIS ACT OF KINDNESS AND MERCY!