Trivia: When Buffy is cheering at the basketball game and Grueller (now a vampire) shows up we see him growling at a player from the other team. The player then tells him "Here, take it" and hands him the ball. The player from the other team (in the red) is Ben Affleck, pre-stardom.
Trivia: Seth Green is one of only two people to appear in both the "Buffy" movie and the TV series. Although his big scene ended up on the cutting room floor, you can see him in vamp-face on the back of the movie box.
Trivia: Because of changes to the script Joss Whedon was forced to make by the studio, he doesn't consider the film canon as established by the TV series. The studio made Whedon trim out many of the film's darker moments, in addition to a quite a few of the jokes he had written. And they also forced him to completely rewrite the climax, which originally ended with Buffy burning down the school's gym to kill the remaining vampires.
Trivia: Amilyn's death scene was completely improvised by Paul Reubens.
Trivia: Joss Whedon's original script, which was drastically altered by the studio, director and cast, was eventually adapted into a comic-book called "The Origin" in 1999. Whedon has said that while he has some small issues with the comic, he thinks it can be viewed as being canonical with the series, unlike the movie.
Trivia: Donald Sutherland reportedly rewrote or improvised much of his dialogue, much to the dismay of writer Joss Whedon. Whedon felt Sutherland's dialogue didn't fit with the script and was at times "unintelligible."
Trivia: Contrary to popular belief, Seth Green is actually not the only person to appear in both the "Buffy the Vampire Slayer" film and series. Actor Chi Muoi Lo also appears in both - playing a background vampire in the movie, and having a small uncredited part in the season 7 episode "Storyteller." While both roles are small (pretty much blink-and-you'll-miss-it), he technically did appear in both.
Trivia: Supposedly David Bowie and Mick Jagger were supposed to have cameos as vampires in the film in one scene, in a sort-of reference to their music video for "Dancing in the Street." Unfortunately, time and financial constraints put an end to this idea.
Trivia: The movie was partially the result of a country-music and pop-culture legend. Sandollar Productions, a studio that helped finance the film, was co-founded by Dolly Parton of all people. Sandollar also went on to be involved with the TV series and its spin-off "Angel." (Though Parton herself was not credited).
Answer: I'd say you treat them as 2 separate things. My personal opinion is that you should just watch the series and forget about the movie.
lionhead