Like when I step away from my computer for a couple of minutes my macbook logs off and I have to log in by entering a password but the torrrents will stop downloading. They will start up again when I log in. Even if I don't have a password to login it still does this so how do I keep my files downloading at all time?

Another question - how do I open my ports so I have faster downloads?

To answer your first question:
Go into 'system preferences' and open up the 'energy saver pane'

Drag the two sliders all the way to 'Never'. This will stop the display sleeping and also the computer itself.
Then when your done downloading return them to however you had/want them.

To answer the second.
I only have experience port forwarding on Windows, but try going to www.portforward.com and follow the guides necessary. Although, quickly looking I see transmission isn't supported. Although Azureus is, so give that a try.

Hope this helps.

I am not a Mac person. I am fairly sure Gonzo84 does not want to do a port forward. I think all he/she is trying to do is allow the controller to pass instructions to the mac. That will allow the mac to speed up instead of using a low default speed. That is most likely a firewall problem.