You can true a wheel a little bit using the brakes as a guide. To get a really good truing job though You need a bicycle truing stand, but you can do a pretty good job just using your brake pads. Check out this youtube videos for help: http://www.youtube.com/watch?v=a25vC5zsf6A
That video shows you how to do it with brakes near the end.
If you want access to a truing stand and you live in the northern suburbs try the bike shed at ceres, they'll be happy to let you use theirs. http://www.thebikeshed.org.au/
In the east the Monash university bikery is also handy.
tips: only do quarter/half turns, and check what has happened regularly. If you do lots and lots of turns you might make things worse, so take it slow.