travelin' man

I have a '98 Accord LX sedan 4cyl. w/AT that had a CEL. Went to Autozone and it showed the P0420 code. From the research I have done there are many reasons beyond the catalytic converter. Before I throw money at this item I would like to rule out the O2 sensor. Has anyone used this software from Harrison R&D (OBDS-Scan, http://www.obdscan.net/index.htm) to monitor the sensor condition/voltages? If not a good choice what about the Equus 3130 Innova? Suggestions?

Also if it comes down to a new Cat. Conv. how are the Magnaflow (#22643) versus the Honda OEM one (About $500 mailorder)?

I reset the ECU, cleared the CEL (removed/replaced fuse 13 in passenger side box, and also the fuse #12 in box on firewall) to see if it will return.

Anything else I should do?

Thanks to all in advance.