Non-spoiler GM notes:
Here are some non-spoiler GM notes (i.e. players are encouraged to read).
The game was based on WOTC's City of the Spider Queen module and the novel series The War of the Spider Queen. The module was written before the novel series, so I made minor updates to keep the adventure consistent with the novels. I also made updates to change the adventure to 3.5 and I removed prestige classes. The characters were based on the AD&D Menzoberanzan boxed set characters.
I also made many story and politics updates/interpretations, as the module is intended for hack and slash adventuring by a party of good characters (with powerful clerical spellcasting) and the author provided almost no guidance as to politics.
The silence of Lolth meant that the priestess characters could not memorize any more spells or recover their turning attempts or otherwise receive power from the Spider Queen.
The module is essentially four chapters: Chapter 1 Szith Morcane, Chapter 2 The Underdark between Szith Morcane and Maerimydra, Chapter 3 the City of Maerimydra, Chapter 4 Castle Maerimydra. I started the adventure in the trading post of Mantol Derith and gave the characters the quest to go to Szith Morcane.
I also incorporated the Book of Vile Darkness (particularly the ArchFiends section and some of the magic items and let Uriel/Kripp have access to BOVD spells). Demogorgon was worshipped by Kripp, various other archfiends had NPC minions. I decided Kurgoth served Orcus for story reasons (minions of Orcus vs. minions of Kiaransalee), but the module never really says what the motivations of Kurgoth are.
House Millithor and Mantol Derith are detailed in the Menzoberanzan boxed set. Mantol Derith has some minor updates in the Underdark book.
I borrowed various FR items from many other sources to give more flavor to the adventure. Randal Morn's sword (now held by Quertus), "The Sword of the Dales", is a quest item sought after by the party in a series of AD&D adventures set in the Dalelands.
Elminister, The Heroes of the Sword Coast, The Circle of Rust and the Worm, the Cult of the Dragon, the City of the Shades, the Church of Bane, etc. are all organizations that are on the peripherary of the main adventure set in Maerimydra. They might or might not have agents in the drow city of Maerimydra as setup by the module.
Where ever possible, I tried to keep actual combat encounters as the same as what was in the module. Although I did make various minor updates: for instance, changing a 3.0 Drow fighter/blackguard in full plate armor with a dire flail to a 3.5 Drow Ranger with a Dire flail in lighter armor.
The Stone Giants, for instance, are specifically noted as attacking drow on sight. Some other encounters will specifically negotiate with drow.
The Balor Badrazel, slain by the party in the final encounter, is in the module as Kurgoth's primary lieutenant. And the only minion that Kurgoth really trusts to operate on his own. He has the power to summon another Balor, so I let him summon Errtu, as that made sense for story reasons, but it could have been any Balor as the module does not specify who Badrazel would try to summon.
Dorina, Solom (level 15 drow wizard), the twin T'sarran priestesses who hated each other, are all straight from the module. The only change I made was changing their spell selection.
In the Lake of Shadows, I kept the Claw and That Which Swims in Darkness sort of the same and made them sort of different. The Claw was a 3.0 half-fiend, I made the Claw a 3.5 Leviathan (Underdark book, special kuo-toa). For That Which Swims in Darkness, the module said he was the tyrant of the Lake of Shadows, but he didn't have a name in the module, so I gave him the name and an attitude. But I left his powers and abilities the same.