I just replaced the broken gear in my odometer, and I thought I would add a few comments in addition to the good resources that are out there on the web. bay13 discusses instrument panel removal at http://www.volvospeed.com/Dashremove.php, and
http://www.matthewsvolvosite.com/odometer_fix.php
specifically addresses the odometer itself.
First off, there seem to be two schools of thought: remove the entire dashboard cover, or just release the left and center, flexing it upward and squeezing the instrument cluster out. IMHO, I would suggest entire removal after using the flex and squeeze method. Maybe I am just getting impatient with age, or maybe it was the additional step of removing the cable to the trip computer (bottom center of the back) that I don't believe was mentioned (perhaps that car didn't have one), that caused me to pull a bit too hard (before discovering said cable was still attached) and scuff very slightly one area of the plastic cluster lens. Also, the odometer reset shaft sticks down, and if you depress it and then pull, it will remain retracted and out of the way and you squeeze by the top of the dash. Once removed, I found a few additional tips that may help the first timer - you remove the 9 screws around the center edge of the cluster that hold the two halves (white and black) together. In addition, I had to remove 4 screws along the bottom of the back side to get the bottom to release. They look like all the other screws on the back, but they are the only ones you have to remove. At this point there are three tiny torx (I think T7) that hold the odometer in from the back. The last suggestion I have is regarding the Turbo needle, if you have a turbo. This needle is the one oddball - it presses on a tiny shaft where all the other needles remain attached to their shafts after face removal. When reassembling, press the dial face as far down as you can to seat it, and then press the turbo needle down as far as possible over its shaft. On my unit, the needle would not stick on the shaft unless I had the needle right up against the face. I relied on attaching the lens to fully seat the dial face, letting the turbo needle swing freely. This was my only choice, and it worked (I had visions of either the needle falling off the shaft during installation or a needle that would never move). The other suggestion regarding turbo I have came from bay13 - it was easy to remove the knee panel under the dash, locate the turbo gauge line and separate it, making one less thing to do when pulling the cluster out. OTOH, I found the elbow easy to remove from the back of the cluster once it was out. YMMV. Again, I really appreciate the work the people did to put their help pages together, and it made it easy to get in there and get the job done. Just wanted to add a few things that I found to possibly help someone else. By the way, I have heard various things about disconnecting the passenger side airbag, and am aware the previous owner of my car did a complete cover removal to replace some cluster indicator lights. He ended up going to the dealer to get the SRS light reset, so maybe avoiding all that does make the squeeze method worth it. It is nice to have the odometer working again. BTW, Groton has the gears for the same price as the manufacturer, but if you combine with other items (like brake pads, disks, etc), you can save decent $ on the shipping. Don 164,543mi and counting. 854T ps I just checked, and neither help page I mentioned had a trip computer. So you folks watch out for the extra small green connector on the back...