I have owned my 03 Giant Iguana for a few years now and it has seen dirt only once. I have ridden it mostly on pavement. It is stock and the frame has not been stressed much.
Lately, I have been doing a lot more mountain biking at Ringwood, NJ. When I get out on the trails I use a Kona Coiler and I love it. It is a little on the heavy side but it's just a matter of getting used to it. I feel like I can do anything with that bike.
Although, the Kona is awesome I feel the need for a lighter hardtail. Would you upgrade an 03 Giant Iguana to do mountain biking and xc style riding? Will the frame support the stresses on that type of riding? Obviously, I'd put quality components on it.
What would be your upgrade schedule? I want to do it gradually.