There are two references to Star Wars Episode IV: A New Hope in Toy Story.

1) When Buzz is describing his "mission" to Woody under the big rig at the gas station, think about what he's saying. Doesn't Buzz's mission sound remarkably similar to R2-D2's role in Star Wars Episode IV? If you don't believe me...

- Buzz Lightyear has in his possession important information that can be used to reveal the weaknesses of a massive weapon that the evil Emperor Zurg is constructing at the edge of the galaxy. He must rendezvous with Star Command to give them this information.

- R2-D2 has in his possession important information that can be used to reveal the weaknesses of the Death Star, a massive weapon that the evil Galactic Empire is using to intimidate and ultimately destroy the Rebel Forces. R2-D2 must rendezvous with the officials at the Rebel Base to give them this information.

2) A smaller and subtler reference... while Sid is torturing Woody by focusing the sun's rays with a magnifying glass onto Woody's head, he borrows a few lines from the scene in Star Wars Episode IV where Darth Vader interrogates Princess Leia pertaining to the location of the Rebel base.

It isn't too surprising that Toy Story would have a few references from George Lucas' greatest epic, especially since Toy Story is Pixar's first motion picture. The programming that Pixar uses to this day to animate their CGI movies was co-created by George Lucas himself in the 80's. Pixar was simply paying an homage to one of the people who made it all possible.