I have an imac 27 with a double boot: snow leopard / ubuntu12.04.
I have to change my hard drive after I make a back up. The last part
is my scary problem.

Could somebody explain me how to proceed ?
Do I have to make a back up for each system/partition separately ?
In that case how should I proceed to restore the systems ?
I know that Time Machine can do the job for mac os system.
Is there something equivalent for ubuntu ?
Is there a way to save restore both at the same time ?

Thank in advance for any help !