Wedding Invitation Wording

I have like two years before my wedding (01/07), but in compiling my guest list I have a question. For female guests whose spouses are deceased... I assume they should still be adressed as Mrs., but that I should not include the deceaseds name (ie: Mrs. Mary Smith vs. Mrs. John Smith). Also, for female guests who are divorced or seperated and dating someone else, should I also refer to them as Mrs or revert back to Ms. Because they are divorced (ie: Mrs. Mary Smith or Ms. Mary Smith)? This stuff is so confusing, any help is appreciated! : )