A.H.
I'm pretty sure you already know that the only way to guarantee the child will be a girl ... is to adopt a girl.
Even the procedures for in vitro fertilization that are supposed to help select a certain gender don't work often enough to be of much help--and are pretty expensive, too.
Consider the consequences carefully before trying to conceive. What will you do if the baby turns out to be a boy? (Even a sonogram is no guarantee--they are still sometimes wrong about the gender.) I doubt that you would love the child any less based on gender, but for some parents, the disappointment may affect their relationship with the child, so don't discount your (or your husband's) desire for a girl as unimportant.
Good luck!
--A.