Which bike for me?

Hi guys. I've been thinking of getting a bike for a while but I'm kinda overwhelmed with all the options. So I will try to tell you what I want and then make up my mind after reading the advice of experienced riders. First of all I rode every day as a kid but I'm 30 now and I haven't had a bike in 10+ years. I'm fairly athletic but have some back problems. I am 6'4" and all legs so I need something tall. I want to ride on the road for running errands (to the post office, grocery store, etc. ; nothing too long distance) and I would also like to do some trail riding. I don't want anything too expensive ($500 range) or too complicated as I am not familiar with all the fancy gear systems, brake types, shocks and such that bikes have these days. I go to REI here in Dallas quite often to buy camping supplies and I always admire their line of Novara bicycles. I haven't bought one yet because I just can't decide which one. So, is Novara a good brand? And what about their Safari? I see it on sale and i like the idea that it would work for the road and the trail. Am I correct? Which other bikes might you recommend? Thanks everyone.