Have you read my reply on your other thread about this, Qwackers? It's hard to help when we don't know which particular French online services you are talking about. If you're looking at the birth records on the Paris Archives website (link below) then you will have to try each arrondissement in turn unless you already know which arrondissement you want. Basically, what you have to do is look in the index first and then when you've found the record in the index, you go to the actual image.
http://archives.paris.fr/s/7/tables-decennales/?
If your husband's grandfather is deceased then you could post up the info that you have and I'll have a try on that website, or if he's still alive, PM me the info.