The best way to get started is to find out if you have a friend, co-worker, or other acquaintance who brews and is willing to brew a batch or two with you. This is ideal as you don't need to buy anything to get started -- your friend will have it all. Of course, bringing a six-pack or buying the batch's ingredients is always a good gesture :). If you find you like brewing your new best buddy can also be an excellent resource.
If you don't know anyone who brews, your next best bet is to get a book or two. I got started when I receieved The Complete Joy of Homebrewing as a birthday gift one year. This book has everything you'll need to get you on your way. Another book option is How to Brew (the first edition is available for free).
I'm not sure which of these books I'd recommend over the other as they are both high quality resources. Check them out at your local bookstore (or sometimes Amazon has a preview of the first chapter or so) and see which you like more. You really can't go wrong with either, or both.
How much do I need to invest in equipment in order to make a decent yield (assuming that's a good thing)?
Most homebrew stores will sell you a starter kit that has all the equipment you need to get rolling plus the raw materials for your first batch. I'd say $200 is ballpark on what you could expect to spend for a decent setup to start.
Leading on from the last one, would I start of brewing a small amount?
Typical homebrew recipes are for a 5 gallon (19L) batch. You can brew larger batches but it requires more costly equipment.
How long does it take to brew a 'typical' home-brew style beer?
There isn't a "homebrew style" of beer. You can homebrew any style of beer you want: pale ales, ambers, stouts and so on. Some of these take months others turn around in weeks. I believe the first recipe on The Complete Joy of Homebrewing takes a total of around two weeks. So I guess the answer is the always helpful: it depends.
I've heard that it can be quite dangerous - what do I have to watch out for?
There's nothing particularly dangerous in homebrewing. You might get some over-carbonated bottles that explode. Aside from that quite a few different cleaning and santizing agents are commonly used in brewing which if misused could be harmful. Read the labels, follow instructions, you'll be fine. If you're unsure ask questions.
And of course any other useful advice to set me off would be greatly appreciated!
Relax. Don't worry. Have a homebrew.