Dual Boot

I have dual OS on my PC and have loaded both Windows 2000 Pro and Windows XP Pro on the same Hard Disk. But over the time one of the OS starts creating problem resulting in re-formatting of the HDD and re-loading of bothe the OS. Am I missing something or is there anyway by which I can have trouble free operation of both the OS. There was an article sometime back on managing dual boot, but somehow it got deleted before I could read and do something. It will be great help if any friend can forward me that article or suggest something concrete.