Ok direct from starwars.com:

Before he became the fat loathsome slug that we recognize Jabba as in Return of the Jedi, Jabba was referred to as a "Hut," and looked quite different. In the 1977 version of A New Hope, there was to be a confrontation between Han Solo and Jabba that was filmed, but it was never completed to make the final release.

The script establishes Jabba to be a large, repulsive creature, an effect that George Lucas could not realize at the time. He is described as a "fat, slug-like creature with eyes on extended feelers and a huge ugly mouth." The scene was filmed with a stand-in actor, Declan Mulholland. It would be over 20 years later that this scene was finally completed. The Special Edition of A New Hope featured a computer-generated Jabba replacement for Mulholland.

In the Marvel Comics adaptation of Star Wars, the confrontation remains intact, but Jabba is a tall humanoid with a walrus-like face, a scraggly topknot, and a bright uniform. The Marvel artists used a variation of Mosep, one of Jabba's underlings, glimpsed as an extra in the Mos Eisley scenes.

There. the Jabba scenes were never finished and never in any version of the movie. So how could these people have seen it in this extended cut? one urban myth ended.

and about the Biggs footage:

http://www.starwarsholidayspecial.com/swcs/episode4/Biggs.html

accept it. this whole "extended cut" of star wars never existed. It is just an urban myth.