Slow rendering is usually due to a complex effect, though it could also be due to a full hard drive. There's no setting for a scratch disk, it'll just use the library's location for render files, if any. RAM probably isn't relevant, but you have more than 1GB! Essentially, make sure your library is on a fast drive with plenty of space and most effects will render quickly. 80GB is not a lot of free space on most drives, though.

Sorry to be the bearer of bad news, but an iMac G5 is very, very old, and can't run the current Final Cut Pro. You might be running a very old version of FCP? Regardless, you're going to see pretty slow performance on a Mac that old. Clearing hard drive space will probably have minimal impact, and at this point you're almost certainly better off moving to a new Mac if possible.

Hi, course author here. If you've put vertical shots in a widescreen timeline, or vice-versa, then you'll probably see black bars on the sides (or the top). The best way to avoid this is to shoot in the same format that you want to deliver, portrait or landscape, and match the project settings to that. If you try to mix portrait and landscape, you'll end up with black bars, or compromising quality by scaling and cropping. If you *do* want to force black bars all the time, you can add an image of black bars on top, or use the Letterbox effect on an adjustment layer. That effect is built for widescreen, though.

While this isn't a Final Cut Pro tutorial, it should show you the basic principles — which are a little time consuming. https://www.youtube.com/watch?v=jraHoC7GGSE