laptops and gaming

I have researched the web, and can't find the answer to a technical
question I have.

I am in the process of buying a laptop, and I have two things that I am
looking for in the laptop.
I want one that is thin and lightweight (under 5lbs including battery).
I also want one that is really good for gaming.

Ideally I should get a notebook with about 1.0 ghz, with 256 or 512 ram,
and a 16mg or 32 mg ddr graphics card. However, these systems always
are fairly big. I can't find a notebook that is lightweight that also
has a great graphics card. All the notebooks I have seen (and I have
probably been to over 40 websites) that are slim and lightweight have
shared video memory, ie, internal video ram. I am wondering if gaming
would still be really good if I got a notebook that had a fair amount of
shared system video ram (ie, 32 or 48 mgs)? In other words, all things
being equal, what is better...a notebook with 16 mgs of dedicated video
ram, or one with 32 mgs of shared video ram? or 48 mgs of shared video
ram? Also, how would 16 mgs of dedicated DDR (such as the Nvidia
Geforce 2Go card, or the ATI card) video ram compare to 32 or 48 mgs of
shared video ram? If you know of a slim notebook that has what I need,
could you refer me to it?

Sorry to ramble on, but I am determined to somehow find this out.
Thanks in advance for any help anyone can offer.