Hi
Unfortunately this won't work for a number of reasons, e.g. FTP, CIFS and RMI port clashes, etc.
There's no problem installing a second instance that's configured to use a separate database (we do this all the time for development jumping between versions) but you can only actually have one running at once.
If you absolutely must have them running concurrently, I'd recommend getting hold of VMware Workstation, or Microsoft VirtualPC and doing it that way.
Thanks,
Mike