AA distance-based award is called OneWorld award. It is NOT a RTW because you dont have to do any RTW, nor you have to travel in one direction. In fact many folks just use it to visit Europe with multiple stopovers at a very cost-effective way if starting from East Coast.
There is an excellent STICKY in AA forum that you should study it thoroughly so you know how to construct your itinerary.
Since your plan is in 2013, you have enough time to prepare for this. Australia is notoriously difficult to book just so you know.
UA has an award literally called RTW, but it is very expensive.
US can do a mini-RTW with regular awards provided you know how to construct it.
I would suggest you to concentrate on AA program as AA miles right now with the mega bonuses still going, you have a bigger chance to amass enough miles. OneWorld STICKY in AA forum is a MUST READ/UNDERSTAND in order to book this efficiently and successfully.
To calculate your miles, keep in mind you cannot use a beeline - for example BWI - SYD, you obviously have to at least transit either at JFK and LAX, (the routing easier to get award seat on QF), or BWI-XXX-DFW-SYD, or BWI-XXX-LAX-SYD/BNE/MEL,... it all depends on how can you find the seats.
The tool to calculate your miles traveled would be this:
http://gc.kls2.com/
You can purchase a low priced domestic one way ticket to get you to west coast for the beginning of your award - thus cuts down 2K miles of distance traveled.
Also dont always think you would need to start / end your award from your home airport BWI. You can easily get to JFK from BWI to cut down the segment / miles used up on your award.
Either you use 25K zone (150C - 150K AA miles in business) for this, or see if you can work it down to 20K zone to reduce the miles required. AA OneWorld STICKY is a de facto Help Thread so you should go there, study up the rules then ask questions.
You can of course combine a OneWorld award with other awards, not necessarily from AA, thanks to the one-way award system that both AA & UA have. Your CO miles will be UA miles effective 1/1/2012 anyway... And your MR would cease to transfer to CO by 09/30/11. So make up your mind before that deadline!