Both are easy tasks for the DIY, just a bit frustrating if you're not prepared. Both take Dexron III A/T fluid... you can buy Nissan Matic D A/T fluid, but it's hard to come by whereas Dexron III is readily available at most auto stores.
9 quarts for the tranny, 3 1/8 quarts for the all-mode transfer case. Draining both fluids is fairly easy, filling them is a pain.
The tranny fluid is drained by taking out the drain plug at the bottom of the A/T pan. It's filled through the A/T dipstick hole, so you'll need a funnel with a very narrow tip (I improvised and fashioned a funnel out of tin foil).
The transfer case has two plugs, a drain plug on the bottom and a filler plug on the rear side (if I remember correctly). Take out the filler plug, take out the drain plug, let it drain, put the drain plug back in. The filling hole is rather high up, so your bottle will probably hit the underbody before it's high enough to pour the fluid into the transfer case. When I changed mine, I actually had to squirt it *up* into the filler hole using the bottle my gear oil came in
(luckly, I changed my diff oil that day too). A small hand pump, $10 or so, would probably come in handy.
I thought I had taken pics but I can't find them; the plugs aren't too hard to locate, though.