The subject line is written to be friendly and get your attention. Melissa, and Happy99 which works much the same way, actually use the name of a person you know because of how it was sent. More on that in a moment. When you open the e-mail, you get a cute nondescript message asking you to open the attached file. This is common.
Viruses have to be opened, or run, to be enacted.
Just opening the e-mail alone won't do it. You have to click to fire it up. There was a short time a while back where screen savers were sent around containing viruses. The big one showed you a small fireworks show and then ate up your hard drive. That kind of attachment is sometimes referred to as a Trojan Horse virus.