Hi dear friends...how can we uninstall ubuntu,linux from the pc...?

hi..thanks for looking at my question...actually i have made a big foolishness to install the OS of Ubuntu linux on my PC which offered me that i would be able to install Ubuntu without making any changes to the PC settings already running with windows xp........ so i installed Ubuntu and realized Ubuntu is of no use and it is a waste one......so i want to have it deleted from my pc......how to delete it....?? now it has been a grate headache for me because it automatically select my OS ubuntu first and taking me to that stupid ubuntu ,yes it waits for some seconds to select OS there where i can select my OS as windows XP but in case if i am not there or somehow could not select windows xp in that few seconds of time, it will automatically select this stupid ubuntu........then i would have to restart it to select my windows XP..........so i want to have this ubuntu removed from my computer....i hope someone will help me out .......anyway thanks in advance.....