I want to break up the strings using a comma as the delimiter.<BR><BR>I want to replace every second bit of white space with a comma. <BR><BR>I tried variations of sed -r 's/ +/,/2g' which does ...

The search string is what you need to alter. You want to replace SEARCH_FOR with the text you're searching for and REPLACE_WITH with the text you want to use as a replacement.