i recommend balance. use the trees -- they aren't a serious threat (damage) to an ice mage, but they are something he has to keep in mind if he doesn't want to loose. abuse cyclone, shift out of freeze effects, don't let your health drop so low that he can shatter you. hearthstone fake him: begin your hearthstone and tempt him to waste his counter spell then you can heal in safety. this requires more time than a real heal, so remember to heal early. if he polymorphs you, shift to something else [quickly].
don't spam moonfire. it'll kill your mana and won't kill him.
double root. root once, he'll blink, then root him again -- blink is on a cooldown, roots aren't. cyclone is a faster cast than frostbolt: if you're low, cyclone first, then heal. save this till later when you need it.
don't use moonkin form: the armor bonus doesn't do you any good and it takes a too much mana to make it worth the 5% crit bonus during such a short fight when you'll be shifting in and out of forms (hopefully travel form because it's cheapest) to avoid snares and freezes. bearform can use feral charge (seriously consider putting spare points into feral for that ability for this duel...) and will drastically increases your health as well as allowing you to use frenzied regeneration if you accumulate a reasonable amount of rage (unlikely, but it will depend on how fast your health drops).
keep in mind: maim. it can't be blinked out of. start the duel in cat (if you don't let him know your talent spec before hand, he may think you're feral) and stay AWAY from his AoEs at the beginning. if you're good, you can run in and get off a ravage before he can stop you, possibly also a claw or shred, but you need to at least rake in order to get combo points. he'll blink, but you shift out of cat (especially if he was stupid and wasted nova right now) and moonfire + swarm while moving towards him and casting lifebloom + rejuv. if he uses ice block at this point to purge your dots, he will very likely first summon his elemental. if he uses the elemental's freeze on you, shift into cat and run towards the mage in order to rake + maim. as soon as he's maimed, try to cast regrowth and then summon your trees on him. now is when you reapply moonfire, swarm, rejuv + lifebloom again and shift into bear in order to charge him -- he will have nova'd your trees into place and blinked away after dropping block. it's important that you quickly build the rage to bash him, possible after a white hit or two (hopefully a crit). this will buy you the time to starfire first and hearth-fake a regrowth second. keep moonfire and swarm applied.
this is all meaningless: everyone has a plan until the shooting starts. i personally don't think you can outlast him -- one of you will get a strong crit and that will be the end. besides, a lot of your time will be taken up shifting trying to keep him from shattering you and healing yourself (do not underestimate the elemental's damage!). he has the gear, you have the instants. i don't think you should have bet so much money on a single duel, coldsnap is likely to just ruin you.
for all the bastards that buy their gold: i hope your genitals rot off.
edit:
consider a build like this:
http://www.worldofwarcraft.com/info/classes/druid/talents.html?50032201253310523005150023010000000000000005002000000000000000
Edited, Mar 18th 2007 3:59pm by FractalSynapse