It also depends on the actual led you're using, how many, color, and several other factors.
Most 3mm or 5mm led's will have a 20ma draw per led, but voltages can vary from 1.2v to 3.5v.
If you're just wanting to change the cluster or hvac bulbs to led's, I'd say go with plug-in bulbs to see if they're the brightness you want.
If you want to change the fog/4x4/headlight bulbs to led's, I'd recommend you send me a PM & buy a set of my custom ones & save yourself some headaches
You can use the resistor values to control the brightness to an extent, but the wrong resistor value will create excess heat or kill the led in a few seconds.
Search around for a resistor calculator online (I found a free one at download.com that works pretty well) this will help determine what resistor you'll need based on the specs of the led's you're using & at what voltage.
Remember that although your vehicle is a 12v system, it can easily produce over 15v which can overpower your led's if they're not properly setup.
I generally calculate my resistors values for max brightness at 14.5v, they'll be a little dimmer at 12v but they have less of a chance of burning up due to over voltage.