The Ghost tool will create an image file of your hard disk in a (usually) compressed format. This image file can be restored to another hard disk should your original hard disk fail, or become corrupted.
There is no capability to execute the image separately directly from your external hard drive.
If you want to create an operational clone of your Win 98 system, you should look at virtual machine software - leading suppliers are VMWare and Microsoft Virtual PC.
It should be possible to clone the image of your Win98 system as a virtual machine image which can then be mounted as a virtual operating system. Note that the virtual environments provide virtual video CPU memory and sound drivers so these images are not easily restorable to physical hardware, so ultimately your choice of imaging or cloning should be determined by what your priorities are. Ghost is ideal for backup, virtual machines are more appropriate for cloning a working environment that you wish to run on another system in virtual mode.