If you have the Windows 98 setup disk that has fdisk.exe on it:
Start the computer with the disk in the drive so it boots from it.
When the program first stops (I can't remember why or what it asks you, I think it is the Windows 98 setup program asking if you want to set up Windows now) press F3 to exit.
When the program exits you should be at a DOS prompt with the A: drive
When FDISK starts you can create partitions or delete partitions, if I am remembering rightly, if you want to have the whole 6GB partition as a single partition I would delete any partitions that may be listed and with no partitions restart the computer with the setup disk in the computer, when you go back to the setup screen, select setup Windows 98 now, and on the next screen you can select to create a partition and format, which Windows setup should do anyway as part of installing Windows.
If you want a few partitions (say 3x2GB partitions) create these following the prompts in fdisk setting one as active and then restart the computer with the setup disk in the drive. Then select to install Windows on the appropriate partition.
If at the beginning you are having trouble booting from the floppy, go into your BIOS and change the boot sequence so that the floppy drive is the first boot item.