I believe it can be overclocked, others have done it. Of course I know it kills battery, but for what gain? How much performance increase would I see in games?
If your notebook comes with GM45 chipset, it's most likely unoverclockable.
I've seen this on 2 notebooks I've sold so far, one with Nvidia graphics, another with ATI graphics. Both are useless for CPU clocking thanks to the infernal Intel chipset and locked BIOS. Most notebooks come with that. And if that's the case, SetFSB is what you want to look at. But be prepared to be disappointed, for you will surely find that the TME has been locked. See this guide
If your notebook has Nvidia or ATI bus controller, then you're in good shape. With ATI you use AMD Overdrive, and with Nvidia you may use Nvidia System Tools.
On one of the notebooks using C2D 2.4GHz, using Nvidia tool I was able to push it to 2.6GHz before it BSODed. So your mileage isn't anywhere near as good as a desktop set. Benchmark wise, for 3DMark06 CPU score I was only able to get from 2101 to 2393. Pretty sad.
Let us know how your overclocking adventure goes.