need serious advice

ok , i have located most of the flaws inherent to a 64 bit xp pro, most prevalent is lack of software to defend it, there are no replies to my first post, my question is this , for a complete linux novice, what is the simplest to install/operate, free, downloadable 64 bit compatible linux system available and where do i get it, ive heard of katana suse fedora but i have no clue who does what , feel free to go into detail , thank you
i am becoming less of a fan of microsloth everyday