Google "Auto Refrigerant". The new R134A is very simple to recharge. The high pressure and low pressure lines have two different sizes and so you can't make a mistake. The low pressure port (where you add the refrigerant) runs along the back side of the engine compartment by the battery and the coolent resevoir.

The gauges on the do-it-yourself cheapo kits are, ah, less than accurate. Plus if you are not in a cool shaded area the settings shown aren't correct anyway. The hotter the ambiant temperature the higher the correct pressure should be.

I would recommend taking it to any decent shop that does A/C work. Most have a fairly inexpensive "check and charge up" service.

If you do it yourself consider purchasing one can with leak detecting dye. If your system is very low it can take quite a while to recharge so don't worry if you don't see anything happening quickly. This is normal. However you should also take care that you don't overcharge the system.

Good luck!