If you want a damn simple and cheap way to train forearms, place two thick books together then try and pinch grip them in your hands. This will burn your forearms, but will strengthen them over time.
Or if you have flat weight plates i.e. no lip, then you can pinch two of these together and that will also strengthen your grip.
A towel wrapped around the handle of a dumbell will also do the trick, and you can either lift with the towel on the bar, or have the two ends of the towel at the top and lift the weight by gripping onto these two ends.
Hammer curls are another good one, though not brilliant.
http://www.askscooby.com/excellent-postings/grip-strength-28609/If you're really struggling with grip, my topic has more in depth information about grip, some exercise ideas, and some products that would easily strengthen your grip.
