I used the extra strength roundup to kill the weeds. Now I have brown weeds that are still rooted in the soil between the paver stones in my driveway. I've been scraping the weeds and moss out with a screw driver but, darn, that's a tedious job. I'm hesitant to power wash them away because I don't want to disrupt the sand and risk the paver stones coming lose.
If I were laying this driveway from scratch I'd use polymeric sand to prevent the weeds from popping up, but alas, the previous home owner was very shortsighted.