Much of this depends on your interpretation of what 'Original Theatrical' means. These films have been tinkered with consistently since they were released.

The quick answer most people go to is the 2006 DVD release Bonus discs. These were officially released by Lucasfilm: http://www.amazon.com/Star-Wars-Two-Disc-Widescreen-Theatrical/dp/B000FQJAIW They are a variation of the movie before the 1997 Special Editions. They are referred to around here as GOUT. 'George's Original Unaltered Trilogy' The source of the GOUT is the 1993 laserdisc transfer.

Next is teh start of investigating the longer answer. Which for people like me, is there is no definitive Original Theatrical version of any of the movies. There are variations. People's values then add weight to which variation should exist on the version they like to watch. So if you want to get into it, it's now about learning what the variations are, where/when they existed and there's a debate there after which gets into what "most" people saw back then.

Star Wars was released immediately in different forms. Mr. Coate has a great article on the subject: http://www.in70mm.com/news/2003/star_wars/index.htm

Variations in the soundtrack presentations of "Star Wars" can be traced to the multiple mixes that were prepared to accommodate the different formats the movie would be released in:

(1) 35mm two-track (four-channel) Dolby Stereo
(2) 70mm Six-Track Dolby Stereo
(3) 35mm Academy mono.

Another SW sound article to read is: http://www.wideanglecloseup.com/starwarsaudio.html

And another Mr. Coate article about SW in '77: http://www.fromscripttodvd.com/star_wars_a_day_long_remembered.htm

What brought about this interest in the OT?