Basically you use the following commands :
select disk 0
clean
create partition primary size=?
create partition primary size=?
create partition primary size=?
select partition 1
activate
assign
select partition 2
assign
select partition 3
assign
exit
Edit the disk number and primary size to your needs. You can insert
theses commands in a .txt script file, and use diskpart /s
you_script.txt to launch you partition edition script. After you use
format tools to format each partition and create a boot.ini that you
place on the first partition.