If you are using a Win98 boot disk, the version of FDISK on Win98(SE) can only cope with drives up to 64GB. From there up, it displays the drive size as (real size - 64GB).
To FDISK using the old version, you cannot put in absolute partition sizes.....you must use percentages.
I can't remember if the WinME FDISK fixes it, but in any case, the new version of FDISK that copes with drives larger than 64GB is available in a link at the bottom of my FAT32 vs NTFS FAQ.