Winamp comes in 2 flavors: Basic and Pro.
Basic is free, Pro is like $20. The main difference is CD ripping and burning speeds. But, also you can encode into propriatary formats (WMA, AAC, MP3 [yes, MP3 is a propriatary format, despite it becoming a psuedo-standard. That is why you have to pay for many mp3 encoders as there are licensing fees to use the format]) with pro.
You do not lose the ability to playback formats or install plugins with basic.
Winamp will play ogg files so you won't need to re-encode.
If you must re-endoce, then get Win-Lame. Can't get any free-er that open source. http://winlame.sourceforge.net/
that, or get winamp 2, that is way better than winamp 5, and can decode/encode from ANY file format.for me, I'll never get rid of my winamp 2.23. it's great.