Osric rulebook (free download) is pretty much a clone of the AD&D 1st edition rules reorganized. I used it for some adventure ideas and for the monster manual. I could easily use my 1st edition books, but it was just as easy to have it installed on the laptop for quick reference. I used Open Office Draw and MS Paint to create simple maps. Open Office makes a great (and free) word processing application. It took me very little time to draw a simple map of the Winding Woods and make ten encounters for the adventure. The kids had a blast playing and so did I. Thomas and I each have two new characters now [3rd level all, dwarven cleric, human fighter, human ranger, and elven wizard]
House rules—we added a few rules to the Microlite20 for our campaign. Charge rule, cover and concealment modifiers, starting spellbooks, surprise, flanking and attack from behind. Just a few extra goodies to add to our game. And best part is that none of it will cause us to dig open the books.