You'll need to use at least version 4.2 of the iPhone SDK
iReddit requires TouchJSON and Three20 to build.
In the parent directory of the project directory, you can check out the requirements with the following commands:
git clone https://github.com/schwa/TouchJSON.git
git clone https://github.com/facebook/three20.git
So your directory structure should look like this:
. <parent directory>
|-- iReddit
|-- three20
'-- TouchJSON
You should then be able to build iReddit.