Before it has even been released in movie theatres, Eminem’s feature acting debut, “8 Mile,” is already claiming the number-one spot — on the music charts. The film’s soundtrack, which features contributions from rappers Jay-Z, Nas and Xzibit, currently holds the pole position on the Billboard 200 and Billboard Top R&B/Hip-Hop Albums this week with 702,000 units sold. The album has been riding on the strength of its single “Lose Yourself,” which also occupies the top spot on Billboard’s Hot 100 chart.

Experts predict “8 Mile” will take the number-one position this weekend at the box office as well. Should this happen, it would be the first time ever that a film’s soundtrack and its single have simultaneously occupied the top spots on their respective charts before that film opened at number one.

The most recent occurrence of anything even closely resembling this phenomenon last occurred when Jennifer Lopez’s J. Lo debuted at number one days after her film “The Wedding Planner” held the top spot at the box office in the first week of February 2001.

The pending success of “8 Mile” and its soundtrack bring to light the increasing prevalence of cross-media marketing in Hollywood. In the simplest of terms (as with Eminem and “8 Mile,” for example), this translates into taking an artist from one medium, establishing him in another and simultaneously reaping the benefits from them both.

Hollywood has long used music to push its movies, and vice versa. Because the movie soundtrack had not yet established itself as a music-market force, early-’60s Elvis Presley films like “Blue Hawaii” and “Fun in Acapulco” were ostensibly used as vehicles to display the King’s vocal stylings and push his music and image. The same can be said of J. Lo and “The Wedding Planner,” as that film’s soundtrack failed to even chart.

As the ’80s approached, and an entire generation of baby boomers who grew up on revolution music and Motown came of age, the movie soundtrack took on an increasingly important financial role in films like “The Big Chill.” Today, it is seen as an essential.

In 1994 “Above the Rim” was received as a middling genre exercise until its soundtrack exploded on the strength of the Nate Dogg/Warren G. single “Regulate.” And after a sputtering start at the box office, “O Brother Where Art Thou?” was helped to a domestic gross of over $45 million thanks in large part to a soundtrack that would go on to top the Billboard 200 more than a year after the film’s release.

On the other end of the spectrum, producers of films with bankable directors and stars look to the soundtrack as a means for supplemental income by using music with which they know its audience will be familiar. The massive success of “Forrest Gump” helped sales of a soundtrack that seemed to gather classic rock tracks at random but ended up a big seller thanks to their carefully orchestrated integration into the film.

The film producers’ dream scenario in this situation is, or course, the movie musical. Using audience’s preconceived genre expectations, producers of a film like “Moulin Rouge!” (its American gross comprised merely a fraction of its worldwide intake thanks to a soundtrack that still holds a spot on the Billboard 200) can approach the marketing of their film from a variety of angles.

“8 Mile,” then, seems to take elements from many of its successful predecessors, combining an Elvis-like appeal for its musician-as-lead-actor and utilizing his established musical skills as a platform for selling the film.

All Eminem has to do is prove himself.