Where can I buy an MP3 encoder for WMP for Windows XP (or WMP9) to encode MP3s with?
This page lists some options. That’s the URL you get shuffled to when you click WMP’s Tools:Options:Copy Music menu dialog’s “Click here for MP3 information” button. Or just upgrade to WMP10, which includes a built-in MP3 encoder. Note that due to Thompson-FhG’s licensing of MP3, you are NOT likely going to find a free MP3 encoder. LAME may have something in the works, but any other package claiming to be ‘free’ is likely pirated software.