Just follow these easy instructions:
Now, when you play an online MP game, hit the zero ("0") command key to bring up the RADIO command menu. From there, select 9 CUSTOM. In my example above, I'll see Avon_Calling listed (without the file type OGG suffix being displayed). Select it and your shout will be heard.
If you need a program to convert a sound file from one format to OGG, your best bet is to head on over to Download.com and search for "ogg converter". You'll find a lot of matching downloads. Make sure you choose one that converts from your shout file's format to OGG.