Try this:

http://www.volvospeed.com/Repair/timingbelt.htm

That website has all kinds of great stuff- for free!

Also, this subject comes up periodically on this newsgroup, and here
is a quick way to the old information:

http://www.google.com/groups?as_q=timing%20belt&as_oq=850%20S70&safe=off&as_ugro
up=alt.autos.volvo&lr=&num=100&hl=en

It took me about four hours on my car a couple years ago.  I
understand the flat rate is about two or less.  Special tools?  The
Volvospeed website describes it in better detail, but you probably
have the hydraulic tensioner which requires a vice (or great big
C-clamp) to compress.  My car had the newer spring kind, which is
described in the UK edition of the S70 Haynes manual.

There are also two or three versions of timing belt on the five
cylinder.  I'd have the VIN number and/or engine serial number handy
when ordering the parts.