As it states right on the website, "Xilisoft Audio Converter provides an easy and completed way to convert MP4 to MP3, M4A to MP3, AAC to MP3, etc, convert audio between popular audio files, such as WAV, WMA, FLAC, OGG, APE, AAC, MP4, MP3, M4A, MP2, VQF etc."
A very useful feature is that you can select the compression method, sample rate, and bitrate when you convert the audio files. This can really help if you have audio files that have a bitrate of 256 or more because an audio file is usually at 128 kbs bitrate and by converting a song that is much higher to 128 it can nearly cut the file size in half, saving you a lot of space on your Ipod or computer.
On the website Click here you can download a free version of the program. One problem with the free version is that is only lets you convert 2 files at a time, so you have to close out and reopen the program, which consumes a little bit of time. It also prompts you with some "Click to Register" windows, but all you have to do to continue using the program is to click cancel, but these are pretty much expected with something that is free. From what I know this program doesn't expire after a certain amount of days, but once again it does only allow 2 conversions per session.