Backing up 2 macbooks on same External HD

[Mberher]

I bought a 500GB external drive with the plan to backup My MacBook Pro and my girlfriends MacBook on the same drive.

Using Time Machine Can this be done? If so How?

 

[simsaladimbamba]

Can be done, either partition the HDD into two partitions, or not, as it is not necessary, as TM will backup the Macs correctly, but for convenience's sake, it might be better.

Time Machine FAQ