When you boot from the installation disc you are given the option to reformat your hard disk. Once you format, follow through with the instructions and you should have one partition with Windows installed on it.
my previous install of wins7 is not fucntioning well so i reinstall it but it seems i did not do a fresh install, instead the 2nd install was piled on top of the initial wins7. so now whenever i start up the pc, it ask which operating i want to use, even though both are wins7. how do i delete the initial wins7??