I'm not actually familiar with Dungeonslayers, but it looks like you will want:
Dungeonslayers 3.5
And that is it.
A lot of these sorts of games have three basic sections; the stuff for the "players," the stuff for the "Game Master" (the player who runs the game, sort of like the host of the show who keeps things humming along), and a "beastiary" that has a bunch of monsters for the GM to throw at the Players. That one document has all of these sections, as well as a Character Sheet (for easily keeping track of character information), and a sample adventure (so the GM has to do minimal work for the first go around).
Whoever is GMing the game might like the Creature Works document (which gives nice reference cards for the monsters), or the Gamemaster shield (which would be set up to hide the GM's dice rolls and to provide them with quick access to a variety of rules and tables), but neither of those are actually necessary.
There are other sample adventures in the Download section, I noticed, so if you and your friends like it, there is a lovely supply for you to take advantage of.
And, of course, if in looking over things you have questions about the game or gaming in general, please let us know. We live to serve (and game).
EDIT: Oh, and you might find Mr. Dr. The Lang's review of the game to be interesting:
http://www.thefreerpgblog.com/2009/03/p ... -kick.htmlIf so, great. If not, then not.