From what I understand, and ID3 tag is at the beginning of an mp3 file. I want to access this data and be able to change it. My question is, would i need a binary stream or a character stream to read it? Put it this way, I wrote a quick program in C that read all the info from an mp3 file with valid id3 tags line by line with a character stream. As you could guess, the results were unreadable, but at the very beginning of the file, it read ID3- and then the rest of the data was encoded. Could I use a binary stream to read this data? or am I missing something?

you can change an id3 tag when you have the song in xmms by right clicking on it and going to file info

You should be able to read it with a character stream as well. You will just have to convert several of the values. But there are different kinds of ID3 tags with different formats. The old ID3 tags are at the end of the file. I suggest if you want an easy way to access the ID3 tags without going through to much hastle you should use the following library: http://freshmeat.net/projects/id3lib

It will do all the messy stuff for you and all you have to do is change some of the fields.