http://www.volvospeed.com/volvo_performance.php has a descreption for a sedan

this is how I did my 96 wagon it might be a little different than yours
since you have a wagon unscrew the screw (torx I believe) by the hook for hanging hangers on in the back
then carefully take off the upper side panels starting by were the tailgate comes down using a flat screw driver (if you put tape on the end it will not scratch as easily)
Be careful these are big and fragile!!!! Once you do that you are home free. Look up and there will be a strut. Have someone hold the tailgate for you (or get on your back and use you leg) and undo the two bolts holding the strut in place. Now just wiggle the strut off the knob on the plate and the knob attached to the roof. Note: there may be pins in the strut to keep them on, these are easy to take off. Put the replacements back on the knobs. secure them with pins (if they come with them, mine did), put the plate back were it was using the bolts, and put the paneling back into place (remember fragile!!!) and don't forget about the two screws.

It sounds like alot but it isn't, but it all needs to be done with the tailgate up (with your leg or someone else holding it)

I got my struts from e-bay motors for 39.09 free shipping they are Scan Tech i believe though not sureand they work almost too good. The door the first time hit me when it opened, even in cold weather. This is a fairly simple thing to do.