I was into modern and classic rock (mostly popular radio stuff) alike before I liked metal.
I got into Maiden through "2 Minutes to Midnight" appearing on GTA: Vice City back in 2002, and promptly picked up the newly released Edward the Great and Brave New World the day after that. Things became a downward spiral after that. I was addicted to Maiden and that basically knocked down the door to classic metal in general. Soon someone on the old Maiden message board turned me onto Stratovarius, which then opened the door to power metal for me. Shortly thereafter Queensryche enlightened me to progressive metal... since then it's basically been just a matter of expanding both vertically and horizontally taste-wise.