first you need to have a Ubuntu 14.04 LTS(latest version) 32bit iso file and next create a live usb using unetbootin
in this link how to create ubuntu live usb with unetbootin
http://www.pendrivelinux.com/using-unetbootin-to-create-a-live-usb-linux/
boot from the pendrive and select "try ubutnu without install"
u will go to a screen like this

there install ubutnu 14.04
continue with your installation untill u see this like in below image

this is very important select "Something else" by selecting this u can select the partition where ubuntu gets installed, after that u will go to

here select your windows 8 partition
identify it with its size, still cant find it then minimize the 'installation window' and press windwos it opens dash type "disks" open disks and see ur windows 8 number under "device number"
then select that partition at the 'installation window' and select 'change' & 'partition type as ext4' & 'mount point as \' & select format
select your hard disk /dev/sda at the "Device for boot loader installation" & install now
it seems too lengthy but quite easy
i hope this helps