If you don't have the Java Development Kit installed and want to install Ant, here are detailed insructions on how to get up and running with both.
Go to http://www.oracle.com/technetwork/java/javase/downloads/index.html and download the Java Development Kit (JDK) You need the JDK and not just the JRE. If you don't know the difference you should probably just download and install the JDK.
Download the Windows version right for your machine/OS. If you don't know any better you're probably okay with the 586.
Run the downloaded file. Accept the defaults.
But make note of the install location
Once the installer does its business you should then see this screen. Congratulations, the JDK is installed.
Now you need to install Ant itself. you can do this following the instructions on the Apache site, but if you want a handy installer, go to http://code.google.com/p/winant/ and "download the latest version". Run the downloaded files.
Again, accept the default options.
Point it to the folder where Java is installed. Select the folder that says jdk in the name.
Tell it where to put Ant. The default is fine.
Restart when prompted
Once you've rebooted, hit the start menu, click on Run and then type "cmd." Hit return. Once the command prompt is open type "ant -version." If it looks like the following, you're done!