What is the point of this macro? And why do you want a macro to automatically switch back to dragonhawk? You should only be in viper for 1 kill in maybe 10. Are you really so lazy that you need a macro to switch for you? A better macro would be one that casts HM, sends pet in, and hits the mob with serpent sting or something like that.
If you are talking about a raiding macro to swap between the two, scroll down and i remember seeing a post about that here on allah, it may be a few pages back by now.
If you want some good macro advice, check out elitist jerks hunter class mechanics, there is a post there about macors that has some very useful 80 Blood Elf (SV/MM) Hunter
Issar 80 Blood Elf (Holy) Paladin
Rinkkel 80 Tauren (Feral) Druid
Agonize 80 Blood Elf (Frost) Death Knight
Bke 80 Tauren (Elemental) Shaman
[The Vindicated]
Raessa 73 Blood Elf (Demo/Aff) Warlock
[Moo]