To allow macs to see other drives other than local ones (see link below), you basically

• edit a setting on your mac
• create a sparse bundle using some unix commands – make it at least 3 times larger than your expected data to be backed up
• MOVE that sparse bundle to a remote machine and connect to that remote directory – then tell time machine to start looking for hard drives.

Here – just do what Stephan says and read with understanding and he leads you through the bullet points above. This stuff is written so you CAN understand what is going on. I learned this stuff long before he simplified it – so thank you.