My car is a 1999. Since most parts of the 1999 are the same as the 1998, I bought the hard copy manuals for the 1998 for brakes, suspension, A/C and wiring. I also have a VADIS disk and a subscription to http://www.alldatadiy.com.
I find the VADIS disk hard to navigate and sketchy. The alldata site is OK. Most of what is on it straight out of the Volvo manual, so the alldata site is never going to be any better than the factory manual.

I have several cars on my alldata subscription ($first one is $25 / year, and each one after that is $15. Renewal is $15, but you have to renew BEFORE it expires. I went to renew on the expiration date, and found that it is considered expired the minute the day begins, so I had to pay $25.) The value of the info is only as good as the value of the info in the factory manuals, but I heartily endorse the alldata solution.