I prefer to download video lectures with download managers. For Real Audio and Real Video streaming lectures I prefer to use NetTransport.

Why? Because it can get the list of stream URLs from a web-page and download them. When you have 20 lectures you don't have to play all of them so that RM Recorder can record them. You just navigate to a web-page with all the links to these 20 lectures, right-click on it and select "Download All..." to download multiple streams!

As for RM to MP3 conversion, please read the following thread
Problem converting recorded Real Media .RM stream to MP3