editing Windows MBR entries

Hi All!Could somebody tell me how to delete the Windows MBR entries??I was installing longhorn on my pc when I had to stop it midway due to some snag.So I got a “Longhorn setup” entry into the MBR that pops up for OS selection everytime I start my PC.Additionally,I had aborted another winXP install after this one & so I can’t complete the Longhorn install now as it is interfering with it.Also plzz tell if I have to delete any additional folders,files etc.