I want to purchase the movie titled "The prince who was a thief"  with
tony curtis.  It was filmed in 1951.

I'm pleased to have been able to help! I am reposting my comment as your answer.

The only way I know to obtain a copy of this movie (which has not been
released commercially) is from a private movie collector who maintains
a website here:

BPM123
http://www.bpm123.net

Bob P. McCready, the collector, lists "The Prince Who Was a Thief" as
one of the videos in his collection:

BPM123: P
http://www.bpm123.net/Moviesp.html

To contact Bob by email, click the link at the bottom of his homepage.

My strategy in locating this information began with Google searches
using the title of the movie plus "vhs OR dvd OR video." Once it
became evident that this film had not yet been released as a
commercial video, I started checking rare film collectors' websites. I
was aware of Bob P. McCready's site from previous experience, and I
was glad to see that he lists "The Prince Who Was a Thief" in his
collection.

Thousands of new titles are being released on DVD each year, so I
wouldn't be surprised if this film hits the commercial market sometime
soon. We are rapidly approaching the time when every movie ever made
will be available to the home video enthusiast.

I hope you're able to get a copy of your movie! This is a fun little
film. Tony Curtis and Piper Laurie are very attractive leads, and
despite Tony's famous Bronx accent, he does a nice job in the title
role.

Best wishes,
pinkfreud

I am very pleased with how quickly and directly my question was
answered.  This is the first time I have used answers.google.com, but
now that I know how great the service is, I'll be sure to use it
again.

The only way I know to obtain a copy of this movie (which has not been
released commercially) is from a private movie collector who maintains
a website here:

BPM123
http://www.bpm123.net

Bob P. McCready, the collector, lists "The Prince Who Was a Thief" as
one of the videos in his collection:

BPM123: P
http://www.bpm123.net/Moviesp.html

To contact Bob by email, click the link at the bottom of his homepage.

Please let me know if this information is fully satisfactory as the
answer to your question.

Thank you for your research.  Your comment does satisfy me as the
answer to my question.

Thank you very much for the five-star rating and the tip!

~pinkfreud

Just to follow up, I did receive a copy of this movie from Bom McCrea
at a great price!

I'm delighted to learn that you've gotten your movie! Thanks for
posting the update. It's always great to have a happy ending.

~pinkfreud