Michael Showalter, who wrote the affectionate summer-camp parody Wet Hot American Summer, takes a stab at directing with this enthusiastic screwball comedy about a dorky tax accountant (Showalter) whose impending marriage to an upper-class china doll (Elizabeth Banks) is complicated by her old flame (Justin Theroux) and an adorable new temp at the accounting firm (Michelle Williams, recalling Shirley MacLaine in The Apartment). Showalter is best known for sketch-comedy shows like Stella and The State, and like that genre, this is sometimes played a little too tongue-in-cheek. But the performers are fresh and offbeat, with the diminutive Peter Dinklage (Elf, The Station Agent) especially funny as a gay wedding planner named Benson Hedges. PG-13, 91 min.