the windows fdisk can only remove non-dos primary partitions. E-smith and some other linux distributions create a small primary partition for the boot partition then an extended partition with ext2 and swap logical partitions within it. Windows fdisk chokes on detecting the non-dos logical partitions so can't delete them. Hence you can't delete the extended partition, hence the first primary partition. You need to use a linux fdisk or something like partition manager. I usually run a Suse install disk, choose a custom partitioning and delete all the partitions then exit the installation when I have wiped the drive.
Tony