The slackware bootable install disks are quite capable of doing this. You boot with two of them (on holds the kernel and the other the root fs), then use fdisk and mkfs to partition and format. One question though . . . why? If you want to install linux then then all install routines I've seen will do this for you anyways, and if it's just for extra storage then you could partition it form you existing linux setup and skip on a bootdisk.