I am looking to get into hitting some local trails here in the burbs of Philly (Core Creek, Whissahickon, Neshaminy) and am wondering what is a decent entry level into the world of mountain biking. This is something I do not know if I will truly like because in all honesty I have never tried it. My fear is that if I buy a cheap(er) bike then I risk the chance of having a lower quality bike make the experience less enjoyable than if I spent the money on something a little nicer. Right now I am looking at the Trek X-Cal 7 as the entry bike but still am iffy to spend that much on something that I might do once in a while instead of all the time as I am imagining. Would I be safe to go cheaper (X-Cal 4) then eventually upgrade components if I take to it?

I know I am talking about entry level stuff here, but I want something that will be enjoyable to ride, and will either last me a bit, or leave me with extra cash to upgrade the parts as I go with what I want. I have test rode both the Cannondale Trail 7/5 and the Trek X-Cals. The geometry on both are fine with me.....so fit is not the issue....just the quality of bike to enter with. What are your thoughts??