Loc: Portland, OR
You could hike on the AT with what you have, but the question becomes: how important is it to you to hike the AT from the start to the finish in one hiking season (aka "thru-hiking")?
If your ambition is to thru-hike the AT in 2013, then you should probably overhaul your equipment at least in part, if not completely, because one factor in a successful thru-hike is reducing your pack weight, which then reduces the physical stress on your body every step of the way. You must get the 'physical work' piece of the equation under the threshhold of what your body can take without breaking down. Getting in good shape so your body can do more work is even more important.
If your goal would be met by walking hundreds of miles of the AT, seeing many beautiful sights, meeting other long distance hikers and sharing thoughts and stories, but not necessarily hiking every step from Maine to Georgia, then you can afford to be a bit looser in your preparations.
But, either way, the first step would be just getting out and hiking, using what you have, learning about your capabilities and getting more proficient. The gear won't hike the trail for you, so it isn't nearly as important as being physically and mentally prepared for months of walking. You can always make adjustments to your gear on an ad hoc basis.
Good luck! Long hikes are exciting to plan and rewarding to walk.
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