his desire to use Pathfinder materials to run a more sandboxy, Old School game. I just discovered this last night. It struck a chord with me because 3e in all its incarnations leaves me cold, but I love Paizo's design style, artwork, and just the look-and-feel they give their stuff. So, how to infuse a more Old School feel into a game that is based on Paizo's rules and Pathfinder adventures?
I offered some suggestions in his comments, and this is expanding on what I wrote there. Generally, what the players want from 3e and its ilk is a sense of story and verisimilitude to their adventures; they don't want to just whack random monsters for random amounts of treasure. What DMs pining for a more Old School game often want is a more open-ended story and a more proactive approach from players towards tackling challenges; they don't want the players twiddling their fingers while they wait for the DM to deliver the adventure on a silver platter. With a creative and flexible DM, those goals are absolutely compatible. (Where you'll run into trouble is the conflict between the players' desire for mechanical customization of their characters and the DM's desire for simplicity. If you find a good way to harmonize those discordant themes, please let me know.)
I don't know any of Paizo's adventure paths well enough to say, but the ones I have read at least make nods towards player choice (and their latest, Kingmaker, promises to do more than that), and as Navdi points out in the comments of his blog, Paizo does a great job of establishing settings that are larger than the mere adventure path and its dungeons. With all that in mind, here are my suggestions to Old School-ify your existing collection of Pathfinder adventure paths:
1) start the players off with a clear, obvious, but open-ended problem. My favorite is a shipwreck (players need to gather supplies and find their way to civilization), but you can also use a natural disaster or alone in the wake of a military defeat for their side.
This works great because the players are presented with concrete, obvious problems to solve, but while there's no dungeon in sight, they're immediately put into the proper, creative, open-ended problem-solving mode that is the backbone of Old School play.
2) Once they've reached civilization, shift the focus to an urban environment. Everyone knows that Old School play and city adventures are incompatible, right? (We just won't mention Aerie of the Slave Lords and Vault of the Drow. Or the Random Harlot table. ;) ) Give them something concrete to do as soon as they get into the city, or better yet, have it be something they need to do that they discovered while solving the issues of the start of the campaign. During the course of this first urban adventure, start planting the seeds of conflict that will inspire the players to make choices: let them hear rumors, find treasure maps, or make enemies that will guide them to your adventure locations. Let them choose sides in local conflicts, and make those choices matter. Most importantly of all, make it clear to them as early as is reasonably possible that their choices have a direct and powerful impact on the setting. If they're not utterly bizarre, they'll love it. And again, that puts them in the proper headspace for Old School play.
Raggi adventure or something from Fight On!
4) By the time the PCs reach 4th or so level, most of the work should be done; they'll be interacting with the world as a place, rather than looking for the markers pointing them towards the next adventure. Don't be surprised if it takes that long, however. Even when the players are all on-board for that sort of thing, it can take some time before they know enough about the setting and the NPCs to really start being proactive and taking their destinies in their own hands.