1. If you have an additional empty partition, you can do the following as root in single user mode.
#fdisk /dev/hda (assumming your hard drive is hda)
type "t" (to change partition type)
type "*" (where *=partition number for the empty partition)
type "82" (82 is the type number for swap partition)
type "w" (to save changes made)
#vi /etc/fstab (to edit fstab file)
add the following line to the /etc/fstab file
/dev/hd* swap swap defaults 0 0
save the changes and exit vi.
#swapon -a
2. Use mkswap on /dev/hd*
#mkswap /dev/hd*
edit /etc/fstab as above
#swapon -a
3. Use mkswap to create a temporary swap file. Do a man on mkswap.