The module is a multilevel dungeon full of the humor and heart so common to T&T products. Some folks think dungeoneering should always be deadly serious, but I find little romps like this to be charming and delightful. What really wins me over is the titular Rat on a Stick restaraunt located in the dungeon. Rules for opening your own franchise are provided!
Since I don't have a copy of T&T, some of the monsters in the dungeon are unfamiliar to me. Most of the baddies are Tolkienian standard, but there are slight differences. For instance, I used a balrog when a "Flame Demon" appeared on a wandering monster roll. The biggest issue when I ran the module were the Black Hobbits. Based upon the text I think these guys are regular hobbits corrupted by evil, so I simply used chaotic-aligned halfings. That led to some wacky hijinx thanks to the presence of a turncoat chaotic halfling in the PC party. If I were to run Rat on a Stick for 3.5, I'd probably use something like this:
Fiendish Halfling, 1st-Level Warrior
Small Humanoid (Halfling); CR 1/2; HD 1d8+1; hp 5;
Init +1; Spd 20 ft.; Space/Reach 5 ft./5 ft.; AC 16 (+1 size, +1 Dex, +3 studded leather, +1 light shield), touch 12, flat-footed 15; Base Atk +1; Grp -3; Atk Longsword +3 melee (1d6/19-20) or light crossbow +3 ranged (1d6/19-20); Full Atk Longsword +3 melee (1d6/19-20) or light crossbow +3 ranged (1d6/19-20); SA Halfling traits, smite good; SQ Halfling traits, Darkvision 60 ft, resistance to cold 5 and fire 5,SR 6; AL Always evil (any); SV Fort +4, Ref +2, Will +0; Str 11, Dex 13, Con 12, Int 10, Wis 9, Cha 8 Skills: Climb +2, Hide +4, Jump -4, Listen +3, Move Silently +1 Feats: Weapon Focus (longsword) Halfling Traits(Ex): +2 racial bonus on Climb, Jump, and Move Silently checks. +1 racial bonus on all saving throws. +2 morale bonus on saving throws against fear. This bonus stacks with the halfling's +1 bonus on saving throws in general. +1 racial bonus on attack rolls with thrown weapons and slings. +2 racial bonus on Listen checks. Smite Good(Su): Once per day a fiendish creature can make a normal melee attack to deal +1 extra damage against a good foe.
Putting together this stat block was absolutely effortless, thanks to YoYo Dyne Technologies' Monster 3.5 program, which takes SRD critters and adds Fiendish and Celestial templates for you. I've also used the Summon Monster statblocks available at that link. Good stuff.