I'm planning on going and have a few questions.
Unfortunately I'll be attending alone and don't know a soul or my way around Canberra. 
What's the best way to get from the airport to ANU?
When I flew up for the 2006 open day, I got my uncle to pick me up, as he lives in Canberra. But I think there might be a shuttle bus from the airport to the city. Google that or Action buses, which is the Canberra bus service. Then print off a map of the city; it's a 10-15 minute walk from the central bus interchange to ANU. Otherwise you could just take a taxi from the airport - might be around $25 or so? Not sure though.
How long does it take to get from the airport to ANU? (I'll prolly get the flight which arrives 9.35am, will I be able to get to ANU by 10.30am?)
Yeah, you ought to. It's a 20 minute drive or so, though the bus would obviously take longer. Why do you need to be there at 10:30 on the dot, anyway?
What residential colleges do you reccomend?
Well I go to Bruce Hall, whereas Eriny goes to Burgmann College. Both are pretty good; Burgmann's slightly more expensive. I'd definitely recommend applying for a catered college to start with, which means one of Bruce, Burgmann, John's, or Ursies. Each has a slightly different reputation: John's is the jock college (+ slutty girls), Burgmann is full of Sydney North Shore (equivalent of Toorak, I suppose) kids doing Arts/Law degrees, Ursies is full of übernerdy anti-social kids. No idea what Bruce's rep is... I suppose each tag is true to some extent, but you're best off going on a tour of each college regardless and decide for yourself. I'll probably be giving tours of Bruce

If you really can't afford catered colleges (which is quite likely; they're really quite expensive), then look into B&G, Fenner, and UniLodge. Note that Fenner is off-campus (2km or something) and, well, quite weird... B&G is quite good though. UniLodge gives you the most room, but is also quite expensive, and isn't nearly as social as other actual colleges.