The magic flac to mp3 free converter is great, i use it to convert that kind of files. Magic FLAC to MP3 Converter allows you to convert FLAC files (Free lossless audio codec) (.flac , .fla, .ogg) to MP3 and WMA, WAV.
MP3 conversion rate suggestions
I'm in the process of converting my FLAC files to MP3's for use on my iPhone. I will be using LAME. What have you found to be the best rate type (VBR, CBR etc.), & rate setting? That is, what saves the most memory, but provides the most acceptable sonics?