Why you need Dual Core processors

I've just been browsing various websites looking at motherboards and processors, in anticipation of actually having money to repair/upgrade daltrey. I was interested to see that the marketing copy for the AMD X2 processors on misco.co.uk explains that Dual-Core processors mean that one core can run my virus scanner, firewall, spyware/adware blockers, etc., while the other is left spare for normal usage.

I'm using Debian and I neither have nor want or need any of those things. Does that mean I can use both cores for real work?

It also mentions that "...now you can simultaneously burn a CD, check e-mail, edit a digital photo, and run your virus protection - all without slowing down your computer". Of course, I'm yet to meet anybody who can do all those things at once; maybe the chip comes with a complimentary second pair of arms.