When you put in the 98Se disk it should ask 3 things, boot computer with cd-rom support, boot without cd-rom support, or install Win98 (I think, I haven't used 98 in along time). Select Boot with CD-ROM support. Once it finishes boot it should drop you at an A: or C: prompt. Type in Fdisk and it should bring you up to the fdisk options menu (since you know you want to fdisk I'm assuming you know how to use it).