I've read that it can be dangerous for your computer to try to run Ubuntu and that the safest option is to run it on an external hard drive. Is this true?
(I don't want to run it through a Virtual Machine.) I would prefer to dual boot it, given that my hard drive has so much space.
Update: So does this mean that even if I have Ubuntu installed, that my data would still be at risk due to, say, stability issues?
It's actually very much possible. There is always a risk of loosing data, so back up first. But it worked well for me. I wrote an extensive guide here. The trickiest part is the work with EFI, since Macs don't have a BIOS. Be sure to check compatibility with your Hardware.
If you want to have the best performance, you will want to dual-boot your machine and use an internal hard disk.
It's not dangerous to install Ubuntu, simply because it doesn't have the ability to hose your hardware, but it can be dangerous to your important data if you don't know what you're doing.
The Ubuntu installer should guide you through partitioning very easily, but it would be wise for you to back your data up first.
