and then i accidentally installed it again
Heh, you
accidentally installed Windows?
The reason you have to choose which Windows to use is because your Boot.ini file can see 3 seperate installations of it. Or more to the point, a new OS has been added to the boot.ini file when it's been installed.
Personally, I would think about formatting the hard drive/partitions and doing a clean install. Do you have any crucial files or documents on the system at the moment? if so, back these up if they are not already.
As for the installation on your E: Drive, if this is just a partition used for data/storage, then you can just delete the folders in this partition which is for the OS (Windows, Documents and Settings etc.) and make sure you have your personal files somewhere in this partition not within these directories.