Problems with disk format compatablility

I use a Win98se computer at home and when I put things on diskette, the disk will not work on 2000 or XP. It always says “disk is not formatted”. How do I get past this? Even when I format the disk on NTFS at work, and download at home from Win98se, it gives same message when I get back to NTFS computer at work. Please can somebody help with this?