Fuel gauge is a very common problem, and basically, is caused by using crappy metal for the sending unit (in the tank). You can try using gas cleaners (Chevron's Techron has been recommended in many places for this), but, it might not work.
For the temperature gauge, go under the hood. On the front of the engine, on the passenger side of the upper radiator hose, you should see a 1-wire connector (the 1-wire should be purple-ish). Make sure that is pressed on firmly to the sending unit.
If that doesn't fix it, it's probably the sending unit (threaded into the block). It's fairly easy to replace (a tight area, but not that bad), and doesn't cost but about $10.
You can try grounding the wire to ground (such as with a jumper wire), and than check the gauge. With the wire to a good ground, the gauge should read full hot. If it doesn't either the wiring is faulty, or the gauge is bad.