Can anyone get a low Body Fat %?

I have a question for the body-builder gurus. Can anyone who eats right and exercises appropriately get to a low enough body fat percentage to look very lean & ripped, or are there genetic traits that just make that impossible for some people? For exercise I currently walk 3 miles 3-4 times per week , but plan to start doing some light weight training 2 times per week starting next week. I have read it's not a good idea to try to put on a lot of muscle during a low-calorie diet. Is this true? I'm just under half-way to goal, but I plan to get into body-building as soon as I'm on a maintenance diet. when I get to goal.  I'd eventually like to have a low body fat percentage, at least lower than "average", whatever that might be. Is this a reasonable goal? Or should I just be happy to get to my goal weight and maintain that? I'm 5'6, and at 150 I'll look "normal" but I'll still be a little soft. And I feel if I can spend this much time, money, and energy to loose 120 pounds, I should just go all out and trade in another 20 pounds of fat for 20 of muscle. What do you think?

Anything is possible.  Shooting for low teen or even a sub-10 body fat percentage is a great goal and very attainable with a strict workout and eating regimin.   

There's a good article regarding body fat percentage here: 
http://www.sport-fitness-advisor.com/bodyfatpercentage.html   
Look towards the bottom of the page for the average body fat percentages of the population and for athletes in different sports.

I haven't done the tape test or the hydrostatic test but last time I got on one of the Tanita scales my body fat percentage was 12.5%.  With a 2% margin of error I'll take that.  :)