This is an old friend and has been doing the rounds for years. This is a hoax. There is no virus. The email is intended to frighten you and turn YOU into a spammer by urging you to forward it to everyone you know.
NEVER forward these shock, horror warnings. They are all hoaxes. Their language is the giveaway and always the same. Your C drive will be erased, pass it to everyone you know and it is, of course, the worst virus ever.
There is an ecard virus - but it has nothing to do with this hoax warning. Snopes explain the difference better than I ever could, so here is what they say:
Although the Postcard virus is real, it isn't a "BIG VIRUS COMING" (it's already been around in multiple forms for a long time now), it will not "burn the whole hard disc" of your computer, CNN didn't classify it as the "worst virus" ever, and it doesn't arrive in messages bearing a subject line of 'Invitation.'
And here's the hoax:
Subject: VERY IMPORTANT - BIG VIRUS COMING !!! PLEASE READ & FORWARD !!!
VERY IMPORTANT - BIG VIRUS COMING !!! PLEASE READ & FORWARD !!! You should be alert during the next few days. Do not open any message with an attachment entitled 'POSTCARD FROM HALLMARK,' regardless of who sent it to you. It is a virus which opens A POSTCARD IMAGE - it 'burns' the entire hard disc C. This virus will be received from someone who has your e-mail address in t heir contact list. This is the reason why you must send this e-mail to all your contacts. It is better to receive this message multiple times than to receive the virus and open it. If you receive mail called' POSTCARD,' even though sent to you by a friend, do not open it! Shut down your computer immediately. This is the worst virus announced by CNN. It has been classified by Microsoft as the most destructive virus ever. McAfee discovered this virus yesterday, and there is no repair yet for this kind of virus. This virus destroys the Zero Sector of the Hard Disc, where the vital information is kept. COPY THIS E-MAIL TO YOUR FRIENDS. REMEMBER: IF YOU SEND IT ON, YOU WILL BENEFIT ALL OF US