Help! MySQL sometimes very slow on Windows 2008

[Robert Lynch]

I am running MySQL 5.5.8 on Windows 2008 Server. I have a PHP shopping cart (Zen Cart 1.3.9h) running under IIS (PHP version on the server is 5.3.4). This project was built by someone else, but now I am responsible for it. I am a MySQL newbie with much more experience with Microsoft SQL Server.

Where do I begin looking for potential causes of severe slowness?

This site sometimes takes tens of seconds to generate and display a page. This happens not only on the public-facing pages with their custom templates, but also on the standard admin pages. I have even seen terribly slow performance at times using MySQL Workbench. (Most one-record inserts say they take 0.015 seconds, but I've seen 30+ seconds on rare occasions.) The poor performance in Workbench is what leads me to think the database may be to blame.

If this topic belongs in the "MySQL Performance" area, I will gladly post it there instead.