Laptop explained

Hi,
yes, this is another 'hey what laptop do i need' question. But what i am really looking for is an explaination how specs translate.
I have currently a desktop with an E8500 3.16 Ghz and a Gforce GT8800. But i want to replace my desktop with a notebook (spaceissues) and look for something what in spec terms can do the job.
But i see mostly lower cpu datas which puzzles me.

The main thing i want to do is a little web/email etc.. but also video coverting H264. codec (using handbrake) and perhaps once in a while a little gaming (Cod4 or so).
My main operating system will be ubuntu with a seperat partition of windows. But windows will be in my case not a big issue.

That said, i seen some gfx chips on notebooks with the nVidia GeForce GTX 260M the more powerful and the nVidia GeForce G105M the weaker brother.
Batterylife i can mostly forget, since the gfx will eat already much of the power.
The cpu Core 2 Duo P8700 seems to be a good choice (25watts) or the Core 2 Duo P9700 (25watts) which is a little more powerful.

What would be a good choice, or is it what you can afford take it.
My pricerange will be around or up to $1500.

Thanks for any tip, i'll appreciate it.