It sounds as if the photos are still on the memory stick.
That is good.
Do not take any more photos on that memory stick until you recover them.

To recover them you will need a memory stick reader.
You can buy them at any store that sells digital cameras ($20).

Then you need some recovery software.
There are literally hundreds of good memory recovery software programs available.
Here is a link to several hundred:

http://www.google.com/search?rls=ig&hl=en&q=memory+card+recovery&btnG=Google+Search&aq=o&oq=&aqi=g10

Choose a program and run it.

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