The email stating that if you get an email titled: "You've received a Post Card" that it is a new virus. Is it true or not?

Where's the email from? If you don't know it, don't open it.

Why should that matter. Who is going to e-mail you that you got a postcard? If its not a virus its another type of scam.

I'm not sure if this is the one to which you are referring, but you might want to check out the information on it on the following site. It could be a virus, if what I am reading is correct.

Urban Legends Reference Pages: 'Postcard from a Family Member' virus

There are places that allow someone to send you an electric post card but usually those will tell you who it's from in the subject area. e.g. Kimberly has sent you an electronic post card. If you have a significate other who might have sent it I would ask them before you open it. Otherwise, if you ever get one, feed to the trash bin.