Normally only with a good antivirus program running and scanning in real time.

I, too, received an email containing the Klezz virus. Only this was from a company called "Umax", who, I think, makes scanners. My Norton caught it and I sent it back to them with a note saying I would tell eveyone not to open any emails from their company.
I tell ya, ya gotta have an anti-virus program running, that's for sure.

And keep it updated.

As an adjunct to my above post. If your system is "unprotected" try this site. Lots of good freeware including an anit-virus program.
http://www.pricelessware.org/

You can´t tell from the name of the sender if the message is infected.
Klez has this as a feature. If your machine is infected, it selects a random address from your address book and replaces the sender address with that. Makes it hard to track down where it came from.

Some people REALLY have too much spare time...

Toni

I fare even worse, My computer at home got hacked, so I got someone installed a firewall program for me. At any night I aam using the computer, there are more than 15 people tring to hacking into my computer, and honestly I don't think the firewall worked that well, because someone did something to my home computer, so I have outlook continously running in the background, and I can not close it, so in 20 minutes I can have 30 outlooks running, then my computer just went dead. So I am not using home computer anymore. If I ever lay my hand on those hackers, I will definitely make them pay!