Depends what you want to do, and what operating system.
If you want to completely wipe the drive then you need to delete all the partitions. If you only want to erase one partition, then just format that partition.
UNless you're running Win98 there's absolutely no reason you should use FDISK.
I'm going to assume you want to do a clean install of Win98 and you want to completely wipe the drive. If so, then just boot from the XP installer CD. Choose a new install and when you get to the point in the installer where it asks you which existing partition you ant to install Windows on, you have the option at that point of selectively deleting and or all partitions. You can also create new partitions. Then you pick the first partition as the install partition for Windows and proceed.
If you just want to wipe the drive before selling it to someone then I would download a free security drive eraser like KillDisk:
http://majorgeeks.com/Active_KillDisk_d4791.html
I use KillDisk Pro myself.
Hope this helps...