Using the preview pane counts - after all, it's got to open the email to display it in the preview pane. It won't open any attachments though.
Simplest thing to do is don't using the preview pane. If you want to open the message, just double click it. If preview's not open, then clicking the message in the summary list will just highlight it.
However, EVERYONE should have a virus scanner installed that checks every email as it comes down from the server. It's so damn cheap - if someone can't afford a virus scanner they've got no business trading.
It's amazing how many people are more worried about getting that new LCD monitor when they don't even have basic security on their computer.