I had this same problem with 1.4 for a while then it just started working one day..

I do everything I did with the other versions, I put the file in lib and click run. The screen pops up and loads some stuff and asks me to press any key to continue. I press a key and it closes out.

Warning: lib\minecraft.jar not found.
Did you read instructions / download it
--------------------------------------------------------------
Error: Failed to run minecraft
JAVA6="c:\Program Files\Java\jre1.6.0_07\bin\java.exe"
Press any key to continue. . .

I did download the minecraft jar from the link given to me, and I put it in the lib file. I checked it several times and it's still there and yet I get this message.