It depends on what numbers you are interested in. There are two numbers that are common to use:
Unemployment number and workforce participation, the first one went down but the latter one also went down.
Unemployment number: This is the number most commonly used and the definition varies what constitutes "unemployed" from country to country. In the US the current number is 7.8% (September 2012), in August it was 8,1% and 8.3% in July.
But in the same time "The U.S. labor force contracted by 368,000 in August 2012 compared to the previous month, reaching 154.6 million. The share of the working-age population, 16 years old and over, that was currently employed or unemployed (i.e., the labor force participation rate) was 63.5%".
So to be clear; to be able to get a lower Unemployment number, 368,000 people had to stop looking for jobs. All in all this is a bad sign for the US economy.
But since this is the official U.S. Bureau of Labor Statistics counts, and has not changed the last few months, the answer must be: No, the current administration did not manipulate the numbers. They told the truth but not the whole truth.