Yes one can install two unsupported operating systems on one hard drive. Google is full of example on how to dual boot Windows and Fedora Core 6 both of which are no longer supported by their respective distributors.
Basic idea, with Windows 98 already installed on the system (or first);
Create somewhere abound 10-gb of blank unformatted free space on the hard drive, boot with the FC6 installation media and install. Linux in genernel can and will use the this unformatted free space to create the Linux partitions needed by the OS.