Barrett Green wrote an answer about Osprey Packs Argon 110 Backpack - 6700-7100cu in on April 21, 2009
First, doing Europe with the backpack rather than suitcase is absolutely the way to go. This is the sort of pack that you should buy for a NOLS course. I would do something different for backpacking Europe. We have used packs that are more geared for "travel" rather than backpacking. They typically have zip off day packs and fewer straps and/or a zip over cover for the hip and shoulder belt so you don't need an overbag to check it without worrying about it coming out of the baggage area missing a shoulder strap.. Osprey makes some targeted at this application.. I have found it better off to organize in stuff sacks/cubes rather than have a lot of pockets on the bag, but that is my organizational style. Good luck. Also might look up Rick Steeves on the web - best "low to the ground" travel guides and his site will have more advice about bags.