You might want to also give a look-see at
MalwareByes.org -- their software is great at cleaning up various malware/trojans. I've found Ad-Aware to not be as up-to-date as their product.
The other great source for all things evil and their fixes on the internet is the
BleepingComputer forums.
They have a tool -
ComboFix - that is also specifically designed to fix DNS hijacking but it too is not meant to be used by the faint of heart as it is pretty sophisticated.
Good luck!