A lot of training to use forklifts is done by the employers. You can get courses in a number of places to teach your employees how to use a forklift safely - but this is something you should take seriously. Don't treat it like a little requirement you're supposed to pretend to meet. Forklifts injure tens of thousands of workers every year, and kill about a hundred. Most of these injuries are caused by untrained workers or people who just don't use common sense. You need both forklift operator training courses as well as forklift safety training for the employees working around them. A number of the deaths each year are caused by employees outside the forklift who get in the way doing something stupid.
You can get a training course online fairly easily. There are forklift safety videos that come with most of them as well.
The Forklift Video Series training program is available online here for $94.47. It comes with VHS tapes, guides to training your employees to be safe when operating forklifts, and a thorough explanation of all the OSHA rules. It's also got a manual for you to use in running the training course, and some tests to give your employees.
Personally, I wouldn't rely on that alone. Supplementing the standard instructional course with your own experience and some other materials is probably the best way to go. There's a good, free online safety course for All-lift.net electric forklift trucks operators with free materials and tests. You might make your employees take that one as well.
For $300 or so, you can also get forklift training software here that will teach your employees safety stuff. The only problem with that is that people who use forklifts don't tend to be the most computer literate - it's not an insult, it's just a fact. If you try to rely on computer tests it's not going to have the same effect as actually getting in a room and talking to them.
The best approach is probably a mixture. Make them watch some videos, make them take the free online course, and then get your most experienced guys to go out there and show them how to do it safely. Showing is always going to be better than telling for most people, but you've got to make sure the guy doing it really knows the OSHA rules and has paid attention to the training courses themselves.
One other cheap way to get these courses is used. Go check out e-bay here and they should have a number of them for sale: