Besides the core books, and the adventure itself, what resources are considered necessary to run the adventure, or to provide background information on the Greyhawk setting.
Any help would be greatly appreciated.
As far as needing more books for background info on Greyhawk, it really depends on which era you would like to play in. Pre-Wars, Wars, or Post Wars.
You can find alot of info at various fan sites, here, canonfire.com, dragonsfoot, etc..
The following are what you are prolly looking for in regards to time period.
Pre-Wars: Greyhawk '83 Boxed Set
Wars: *From the Ashes Boxed Set
Post-Wars: Living Greyhawk Gazateer
*(Technically Post-Wars, but enough info to run during wars era)
Now, as far as which era to recommend? Have at it boys...
For example, if your PCs know anything about the wars and the effects of the wars then pre-and during wars campaigns either require you to follow some rather world shaking events or ignore them and then explain why something did not happen. In any case, it is more work to do the pre-wars stuff if you expect your campaign to follow the published stuff.
As far as more diverse adventuring, come on raiding the Old One's holdings, working with evil to defeat evil for the greater good...a DM's dream! AND A PLAYER'S NIGHTMARE
It's hack'n'slash gone mad, with a fairly weak and rather ineffectual set of justifications, and worse, very weak and very ineffectual adventure hooks.
Other than that, it's a fun adventure if you're looking for low roleplaying, kick in the door, kill everything, loot, go back to town, stock up, rinse'n'repeat kinda game.
Personally, I think it's better used seperately as various dungeons and encounters that can be utilized within a campaign of your own creation. It has some spiffy maps and locations that are well detailed and some neat treasures. But as a coherent campaign... it's lacking.
And personally, I'd recommend post-wars. That way you get to use all of the great Carl Sargent material
