you should be able to install into a new directory, can be on the same partition. you'll need setup disks, and you should make a boot disk and modify the boot.ini file. you should keep a boot and erd disk and understand how boot.ini works. you can get instructions on this stuff at
www.microsoft.com/support - search Windows 2000 for "boot disk", "boot failure", etc.
once you get the second install up, you can attempt to fix the first install, or just use the second install, but it means starting from scratch and some leftover system files, but no data lost.
As a MCSE consultant, I'm advising all of you to not install software until the first service pack is released, at least not on a production machine.
My .02