there's tons of stuff I can point you to so you can play ogg vorbis on windows.
re-encoding is generally a bad idea with lossy formats, especially from a good format to an inferior one..
winamp supports it natively...
a directshow filter here
there's an itunes addon for it here
an addon for nero here
a windows shell extension for editing and viewing tags and info n' such here
unless you have a better reason to need mp3 these should serve you nicely.
it IS open source and cross-platform..