RF Modulator for 2000 Altima?

Are you comfortable with soldering and/or crimping wires?  Any method you use will require you to do this.

Does the vehicle have steering wheel stereo controls?  If so, the recommended method of hooking up a modulator is to find (in the radio's harness) the 12 volt constant and switched wires, strip off some insulation from the appropriate wire, and solder on the corresponding wire of the modulator.  Then just tape up the wire and repeat for the next wire, until you've done all the wires of the modulator.  Most nissans don't have a ground wire built in to the radio's harness so you'll have to ground the modulator to any bare metal bracket or support behind the radio dash opening.

If your vehicle does NOT have steering wheel audio controls, you can buy a harness ( Metra 70-7550 or equivalent) and reverse harness ( Metra 71-7550 or equivalent), solder all the wires (except the yellow and red wires) for both harnesses together so that you're basically left with 2 nissan male plugs on one end, and 2 nissan female plugs on the other end.  The reason I said to not do the red and yellow wires just yet is because the modulator's wires are going to be hooked up to the same corresponding wiring color's connection point.  It's just easier to solder all three yellow wires together at the same point and at the same time (same thing goes for the red wires too).

This method using harnesses and reverse harnesses is easier than the first method of tapping in to the factory harness, because you do not need to test the factory wires and figure out the factory wiring colors; also, once you're done you just plug everything back in to the factory wiring for a clean, easy hookup.  And of course you'll also need to ground the modulator's black wire as well in the same manner I described above.

Most likely your car has the diversity antenna system, and you're going to need two antenna adapters:  the nissan diversity antenna adapter, and the reverse diversity antenna adapter.  You can get them both together from Scosche, or just buy them individually from metra or any of the other kit companies out there.  Your local best buy or circuit city should have them.  If your car does not even have the diversity antenna system then you won't even need any adapters.

Is this the Sony xm radio unit that's the portable one and goes in that little cradle thing?  Or is this the unilink (hideaway) tuner?