The processor in centrino systems is the "Pentium M". "Centrino" merely means that the computer uses specific intel hardware including, among other things, the pentium M cpu and intel's wireless card. Not all laptops that use the pentium M cpu will be labeled as centrino systems due to the way intel restricts the use of the centrino brand name.
The Pentium M is clocked at a lower speed than other intel processors but it is more efficient, so a 1.6 ghz pentium M will run about as fast as a 2.4 to 2.6 ghz Pentium 4 while being vastly more energy efficient.
The fastest pentium M processors are currently 1.7 ghz and intel is supposedly going to be releasing a new version of the pentium M sometime in the next few months that ought to be faster and even more energy efficient.
The pentium M processors aren't the absolute fastest notebook processors available but they are almost as fast as the pentium 4 cpus and will use less power and run cooler so the laptop doesn't get too hot. A 1.6 or 1.7 ghz Pentium M (or "centrino") laptop matched up with an ATI mobility radeon 9600 video chip would make a fine gaming laptop without sacrificing too much battery life.
There is a celeron version of the pentium M but it has half the cache memory as the regular pentium M and more importantly, has a lot of the energy saving features disabled so it uses up the battery a lot faster. The pentium M celeron is only a little cheaper than a regular pentium M so there is no reason to buy a celeron powered laptop.
