Faq has information about the hall sensor. It looks somewhat difficult- but probably not so after you've done it once. You have to get into the innards of the distributor. I have the same problem, except my car dies when I am driving, sometimes when I come to a stop. It isn't as frequent as yours either (1-2 times a week... until I quit driving it, it may be worse now). I opted to replace the entire distributor- about $100 more I believe. BTW, you could find a hall sensor somewhere on the internet for much cheaper I bet (fcpgroton.com, alloemvolvoparts.com etc). The volvo dealer in mine town wanted $270+tax for a dist. I got it on the internet for $170 with free ship and no tax.
Good luck,
Nathan