HLW

I'm saving up to buy a new computer with Windows 7, and I want my computer to be completely secured and protected from EVERYTHING that is/can be harmful to my PC.

I want a security program that protects EVERYTHING I have on my PC, and nothing that will merely eat up all of my hard drive's free memory space.

So... Which one is the best?

And another question: Is it possible to have more than one security program on one PC?
And if possible, please be detailed with your answers!

Like, describe the program you think is best; like how much space it requires, what it comes with, etc.