The 1e AD&D DMG is the Julius Ceasar of RPG books. Get it. Discover AD&D, and I guarantee you'll be into it. The book is well written, with lots of room for the DM to customize. It also stresses the power of the DM as opposed to the power of rules lawyers and munchkins, which is really great. The book is pretty easy to understand, and the system can be learned within an hour of actual play.
Pick up a copy of the 1e PHB as well.
If you ever feel like running a well fleshed out AD&D campaign, which I'm sure you will after reading the DMG, you can match my library to give your players tons of options:
1e AD&D DMG
1e AD&D PHB
1e Monster Manual 1 and 2
1e Unearthed Arcana
1e Oriental Adventures
1e Fiend Folio
2e DMG
2e PHB
2e Montrous Manual
Basic and Expert Rulebooks
Hackmaster PHB
Hackmaster GMG
The Arcanum (Bard Games)
Dragonfist
As many Old School Modules as you can find (I have about fifty)
All I really want now is a Rules Cyclopedia. The most expensive books out of this whole collection were the HM books, and that was only about $25 each. All of this stuff is interchangeable with only minor conversion. All in all, I spent about $120 total.
Also, if you use Castles and Crusades, you can easily use all of these products as well as your current 3.whatever products. I don't do this myself, but alot of folks do. And the Castles and Crusades books are pretty cheap too.
I hope you enjoy your book, and welcome to the one true system. Even if you're only browsing.
IF you want a good online resource if you aren't understanding parts of the DMG, go to The Acaeum or dragonsfoot.org
