If at all possible leave the asbestos in place and go over it. If done properly this will be just as good as completely removing it. If the old vinyl flooring is in good shape and you just changing because you tired of the old floor use an "Embossing Leveler" and skim the old floor to make it smooth for the new floor. If the old flooring is in bad shape install 1/4" underlayment over the old floor then your set. Whoever installs your floor should be able to make the call wich route is best in your application.