Do you have a working GS system disk? If you do you can format the disks with that. If not do you have a copy of ADTPro to use to transfer images between your PC/Mac and the GS? If you have the latest copy of ADTPro, 1.0.2, it has an option to format the disk for you. If you need it you can download it from here:
http://adtpro.sourceforge.net/
hope this helps.
Magnus
http://adtpro.sourceforge.net/
hope this helps.
Magnus