Temp Guage + Check Engine Light

My wife has a 1999 Jetta GL (the newer looking model). The car is an automatic, about 100,000 miles. It has a 2.0 4-cyl engine.

The car started leaking anti-freeze, somewhere on the right side of the engine. The check engine light is now on. Very shortly after turning the car on, the temperature light goes on and beeps a few times. The temperature gauge acts stupid the whole time the car is running. Sometimes its on 0, sometimes its in the middle, sometimes it goes all the way up and we freak out and shut the car off before it gets in the red. Does anyone know what could be causing this? Because apart from all this junk seeming to be wrong, the car still runs pretty good. Also, just to be sure I replaced the thermostat. (that wasn't the problem). Any help would be greatly appreciated. Thanks!

The temp light flashes when the coolant level is low. The gauge may also give erratic readings when the level is low. If the leak is on the car's right side by the belts, then I would guess water pump failure. Get it looked at asap.

Thanks for the suggestion. I'll check that out. Do you or does anyone think it could be anything else? What about a head gasket? Could that cause the same syptoms or would I notice something more?

It's possible, but not as common. You should have it pressure tested to pinpoint the leak. Another common leak area is the plastic flanges that attach to the cylinder head where the hoses connect will crack internally and leak.