My heat and air only work on the highest setting?
Anyone have any ideas?

I think it's designed that way actually. Xterra A/C's have this random operation function. In my brand new 2003 you couldn't turn off the A/C and that was correct according to Nissan, so I'm sure yours is too.

You may find some other opinions though if you search a little.

If you mean that the blower only runs at the highest setting, you need to replace the blower motor resistor assembly.

Anyone have any idea how difficult it is to replace a blower motor reistor assembly? Hard to get to? Price?

Look up under the dash on the passengers side and find the bottom of the blower motor. Near it you'll see a connector with several wires, mostly blue. Remove the two screws on either side of the connector and the resistor assembly will slide down and out. If you removed the right thing it will look like a thin rectangle of ceramic.

They're around $15.

So, which is easier...

Saying "blower motor resistor assembly" or replacing the blower motor resistor assembly?

Okay, I'll be quiet now.

Local dealership charged me $15 for the assembly. It took about 20 minutes to replace and I was taking my time.

It certainly takes longer to describe where it is than it does to change it.