1. Put your song into your public dropbox[dropbox.com] folder.
2. Right click the song and select 'Copy public link'.
3. Paste the url into the website's[fgtradio.fgthou.se] url field.
4. Fill out the artist, title and genre fields also.
5. Click submit.

MAKE SURE THE MEDIA IS IN YOUR PUBLIC FOLDER!
IF YOU GOTO YOUR OWN LINK AND IT ASKS YOU TO DOWNLOAD OR ADD TO MY DROPBOX, THATS NOT THE CORRECT LINK TO SUBMIT.

Wall of text edition below:
Adding your own music is somewhat simple. First you'll first need to upload the songs you would like to share with everyone to dropbox, or some other file sharing site that allows hotlinking.[simple.wikipedia.org] For simplicity I'll be showing you how to do it with dropbox.

Open up your dropbox application and then goto your dropbox folder. Then in your dropbox folder there is a folder called 'Public'. In the public folder is where all your music will need to go. If you want to be organized you can create a folder inside here and put your music in that. Once your music has finished uploading to dropbox you'll need to put it into the radio's database. To do that right click on the song in your public dropbox folder and click 'Copy public link'. Then head over to http://fgtradio.fgthou.se and click 'Add New Song' in the top left. Paste the public url into the URL form. Then fill out the title, artist and genre forms too, click submit.

From what I've tested the radio will play mp3/mp4/ogg and if you have quicktime installed anything quicktime will play itself.