Yes, for myself, an internal hard drive was the better choice. I've heard that external hard drives don't operate as fast as an internal one. As far as installing one, the manual that came with my G4 shows you step by step how to install an extra hard drive. My problem came in setting it up so that it would show up on my desktop. I ended up calling the manufacturer of the hard drive I bought and they told me what to do.
If an internal hard drive is what you want and you're not sure how install one, you'd probably better have someone do it for you because it can be tricky, especially with all the wires and complex riggings inside the computer. I'm not saying that an external hard drive won't work because they do, and they work just as good as an internal,
but I was concerned about the speed issue of the external as opposed to the internal. If you'd rather have an external, they're a lot easier to install the an internal.
Good luck on your choice.
Tunesman.