I'd load up CPU-Z to see if it gets the same results. Does the bottom get rather hot when running? If it hasn't been blown out with a can of air in a while, it could be throttling back to protect itself and if the fan fins are dirty, it starts out that way and never leaves that state.
A little late, but I figure I'd let you know. I have the same laptop. The processor is a 1.76ghz, but dell set it up to stay locked at 800mhz, apparently so extend battery life. I came across this thread while looking for info on how to change the settings, and run at full speed.