I'm a BIG FAN of trail running... and actually lived and worked in Boulder several years ago where I ran trails exclusively... not sure what part of CO you're in, but I'm sure you're probably pretty close to some amazing trails...
It sounds like from your post that you're not already running? If that's the case I might suggest starting with one of the walk-run-walk-run type programs like the various C25K programs... and just find some easy and relatively flat trails to do it on at first... then once you're comfortable with that you could try some more difficult technical single-track if you feel up for it... and don't be afraid to walk whenever you need to... in fact, depending on how steep it it is sometimes power walking it is a lot faster and more efficient than trying to "run" it...
As far as "trail" running shoes go... you may not need such a specialized shoe unless you are going to be running on pretty technical trails... and actually, a really good running shoe that's right for you can get the job done pretty well... I only use a "trail" shoe for very technical trails with single-track and rock scrambling... where the extra stability might come in handy... So I actually do most of my trail running in a pair of "road" shoes that work well for me... but when it comes to trail shoes I've always been partial to Montrail's because they are what works for me... but that's purely personal preference... My suggestion there is to go to a good running store and tell what you're looking to do and get fitted... like I say you may not need an actual "trail" specific shoe at first... personally I think the right fit for your biomechanics with the right amount of stability and cushioning is more important than getting a trail specific shoe at first if you're not going to be on really hardcore trails... at least just yet...
Hope this helps... and Happy Trails! (Sorry for the really bad pun... but sometimes I just can't help myself...
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