Different OS’s on partitioned HD

I am running a 1.9 Ghz amd processor with 350+MB of Ram and have an 80GB HDD. The HDD has 5 partitions, each one with a different OS on it. I installed Win98se, Win2KPro, WinXP pro and another partition for backups. My problem is I cannot get Win MEinstalled onto the remaining partition. For whatever reason it keeps telling me that another Wnndows OS has been detected and suggests I purchase the upgrade disc as opposed to the clean install disc I am trying to install.I know there is meant to be a way to remedy this that involves disabling some startup files on the other OS’s. Could anyone be so kind as to let me into the secret or alternatively give me another type of answer to my question.