Well, for starters, don't look at the System Properties to determine CPU speed; it's very often wrong. For example, right now it claims that my processor is running at 367MHz, when in fact it cannot go lower than 800MHz.
Is your laptop running at full speed while on battery, or do you have it on A/C power? Chances are that the default power setting is configured so that the processor runs at maximum performance on A/C, but clocks down on battery. Also, have you changed any power settings in Windows, or switched to a different profile?