Lots of people using Microsoft Security Essentials, Norton, AVG and others with no major issues.

If things are very slow for other web based activity at the same time, then it does point to an actual problem and the result might be a symptom of an actual problem.

There are files of known sizes at http://www.thinkbroadband.com/download.html with guideline times to download

Sorry, I don't understand what you mean by "an actual problem"!

You said '(when things are snail's pace on mine, they generally are on his too)' which suggests that there is a problem beyond seeing zero from the speed test result.

That is what I am trying to establish, is there a slow speed issue in day to day use of your connection, or am I trying to figure out why our tester on a PC configuration that I have zero information about is not working.