If you download files from archive.org's audio section, you probably observed by now that, while there are options to download all the files in 64Kbps or variable bitrate MP3, there is no ogg download of the same type.
Don't forge ahead right clicking all individual ogg downloads, we can get some open source software to help.
For example purposes, let's pick some Blind Willie McTell music. There are only three songs there, but it should be enough for you to get the basic idea.
The first step is quite simple: we need to get a list of links towards those ogg files. If you're using Firefox, all you need to do is to expand the list of songs on the left side of the page, under the MP3 zip downloads, then select all its text, right click it and choose "View Selection Source". It's a bit complicated to explain, but this screenshot should help:
If you aren't using Firefox, just open the source of the page (CTRL+U in most browsers) and search for the first instance of the string ".ogg". It should occur around line 222, and nicely included in some divs will be that list of links that I was referring to.
Just copy that bit of html and pop it into a text editor of your choice, then save it, call the file "links.html" for example. And now for the real action, let's call upon that open source help. It's something along the lines of:
wget -Fi links.html -B http://www.archive.org
What we're doing here is asking wget to download all the files referred to in links.html. The catch is that the links are relative to the server root so, with the aid of the "-B" parameter, we're basically telling wget that the server is archive.org.
That's all, hope it helps someone!