The Bay 13 write up on this is excellent, all of them are really. The only problem I ran into was the torx bolts securing the bearing assembly to the hub would not come off with my impact gun. So I took that to a shop, zoom zoom and they were off. Autozone has Timken bearings for the 850.

The front wheels are the same on the AWDs as the FWDs. Here is a good place to start:
http://volvospeed.com/Repair/FWDbearingHub.php

There is other info available online if you search around a bit.

It's not a really tough job as long as things aren't rusted up too badly.

I would buy a can of good penetrating fluid (PBBlaster) and spray your axle nut, the four torx bolts, in behind the rotor, and around the back of the hub where it fits against the carrier (from behind) every day for a week leading up to the operation to make disassembly as easy as possible.

Stuck rotors can often be displaced by loosening the lug bolts 1/4-1/2 turn and then driving to the end of the driveway and slamming the brakes really hard.

Get a bottle of antiseize for reassembly and use it on everything.

Take your calipers apart while you're at it and clean and lube the sliding pins with a good brake grease.

Also a good time to do sway bar end links if they're bad (and they often are).