I have my first Mac after many years with PC's, an Imac G5 20", and
would like to know which are the best choices for interfacing internet
radio on this computer.  I prefer access to talk - talk science, talk
business, talk Air America Radio.

itune should already been loaded on you system, if not load you iLife
CD which should include all the Mac software. You also can download
this from apple. Once you start the program on the left side of the
program you will se you options, radio is one of those options. select
radio then the right side of the screen will change. select you
channel(program type). FYI your computer would need to be connected to
the Internet - you knew this but I thought I might add. To select
program double click on the program title > then select station. You
may have to sample a few to find you favorite