As andrewclaus said, not sure you really need to disconnect the battery for that job, because the blower and resistor only get power when the key is in the ON position. Leave the key out of the ignition and you'll be fine. However, its easy, and and go ahead and disconnect the battery negative terminal if you want. The stock radio should remember the station presets but you'll need to reset the clock.
Always disconnect the negative battery terminal first, I speak from personal experience. When you disconnect the negative terminal, if you're clumsy and your wrench touches the negative terminal and the car body at the same time, nothing happens. Once the negative is disconnected, if you are clumsy and touch the positive terminal and the car body, nothing happens because there is no longer a path to the negative terminal. However, if you go to disconnect the positive terminal first, and are clumsy, and the wrench touches the positive terminal and your metal watch band (or ring) which is resting on the car body, the current has a path from the positive terminal through the wrench, the watch band, and the car body back to the still connected negative terminal, and the resultant high current will instantly heat your watch band giving you second degree burns, and may arc weld some of those metal things together.
