Ok I'll tel u
Open Winrar
Within winrar go to the files u want to add
select those files
use Ctrl button for multiple select
now right click on selected files
and say add to the archive

A box will popup
Give the location to save the splitted archive
In that box at left bottom u'll find
"split archive into"
If u want select a predefined setting or
type the volume size to split
U want to split it into 70Mb
for safety keep it 69 MB
so enter the size as 72351744
and say ok

Now go to the directorey u chose to save

u'll find 2 archive if all went right
It takes time so hav patience