May be you use an old version of LimeWire.
.Ogg files are already now in the list of audio files that are searched by default...

The current default list of extensions searched for each category is here (Java source file):

MediaType text = new MediaType(SCHEMA_DOCUMENTS, DOCUMENTS,
new String[] {
"html", "htm", "xml", "xhtml", "txt",
"pdf", "ps", "eps", "rtf", "doc",
"tex", "texi", "latex", "man"
});
MediaType programs = new MediaType(SCHEMA_PROGRAMS, PROGRAMS,
new String[] {
"exe", "bin", "sh", "csh",
"zip", "arj", "rar", "lha",
"cab", "rpm", "deb", "msi", "msp",
"gz", "gzip", "z",
"tar", "tgz", "taz", "shar",
"hqx", "sit", "dmg", "7z"
});
MediaType audio = new MediaType(SCHEMA_AUDIO, AUDIO,
new String[] {
"mp3", "mpa", "ogg", "wma",
"ra", "rm", "ram", "rmj", "lqt",
"wav", "au", "snd",
"aif", "aiff", "aifc", "mod", "med", "iso"
});
MediaType video = new MediaType(SCHEMA_VIDEO, VIDEO,
new String[] {
"mpg", "mpeg", "mpe", "mng",
"rm", "ram", "asf", "qt", "mov", "avi",
"swf", "dcr", "jve", "nsv"
});
MediaType images = new MediaType(SCHEMA_IMAGES, IMAGES,
new String[] {
"gif", "jpg", "jpeg", "jpe", "png",
"tif", "tiff", "bmp", "ico", "pcx",
"pic", "pbm", "pnm", "ppm", "xwd"
});