|I had tried that (or something similar) before, but it didn't work.|
If you had tried my formula you would have seen that all it does it cut the beginning of the string, starting on the left side, up to the space character.
It then takes that string, which in your example is 5/31/2011 and converts it to a real date with the format of yyyy/mm/dd.
The string PDT at the end would have no affect on the formula.
You did not specify you wanted to retain the time.
But, I'm Glad you solved you problem, and shared your solution.