Did you know that its actually possible to type ergonomically without using an ergonomic keyboard?
Although an ergonomic keyboard makes it much easier, there are tips that you can follow to make your own typing more ergonomic without buying an ergonomic keyboard.
First, be sure to always pick your wrists, up, like you're playing the piano. You should only rest your wrists when you're not actively typing.
Secondly, touch the keys lightly. There should be no need to bang on the keys to get them to work, and if there is, you need a new keyboard.
You also shouldn't stretch your fingers to reach keys that are not within your natural finger reach -- move your arm instead.
Finally, try to keep your hands and fingers relaxed. The more you are able to keep them in a natural position, the healthier your typing will be.
Of course, I'm not at all decrying ergonomic keyboards -- they work great, and are excellent for healthy typing. However, if you're stuck without one, there are still things you can do to improve your typing health and reduce your risk of repetitive stress disorders and carpal tunnel syndrome.