Hi Jim,
If it's any help, I prefer to use third party software to convert to mp3. My thoughts are that this give me greater control over the quality of the final product. There are heaps of freeware programs available to do such conversions. The link below explains how I go about it use a program called "Free Audio Converter".
... link to converting to mp3 using FreAc.I've used variable bit rate (VBR). If you activate CBR instead of VBR, then constant bitrates will be produced (for example, 128 kbps at 44.1 kHz).
Hope this helps,
Noel
P.S. If you choose to install FreAc (or any freeware for that matter), watch out for the free toolbars, etc., that often accompany these installations. To stop any unwanted installations, choose a "Custom Install" (if available) and then deselect anything that looks outside the program (e.g. Ask.com toolbar).