The most critical component for gaming (without drastically lowering the game settings or not being able to play many games at all under 64mb dedicated video -- don't even think about shared/integrated video memory) is the dedicated video card.
If you really want to play Doom 3 or Half life 2 or any other new modern game on a notebook (which can't be upgraded later for the video card -- it it is fixed and it is soldered in to the motherboard) get:
The Dell 8600 -- this is a 15.4" widescreen notebook that weighs 6.9 pounds with the Pentium M processor for better battery life (and built in wi-fi). Get at least the Pentium M 725 1.6 Pentium M processor (Centrino) or above.
This Dell does not have great keyboard, the case is too plastiky and thick for the Pentium M processor, etc but it has the ATI 9700 video card with 128mb RAM you want. You can get this on 17" LCD Pentium 4M desktop replacements like the hpzd7000 (see zd7000forums.com) or the Toshiba 17" Pentium 4M (at under $2,000 also) but they run too hot and have horrible battery life (under 2 hours).
The Dell 8600 should get you at least 3.5-4 hours using wi-fi (internet surfing over DSL or Cable) and up to another hour or so not using wi-fi. Games using the hard drive alot may only be 3 hours or less but that will still be 2x or more what you will get with a Pentium 4M. Get the Hitachi 7200rpm hard drive option for screaming fast (up to 70% faster) seek time versus a stock 4200rpm notebook hard drive.
There are many better Pentium M notebooks out there (or even Athlon 64 notebooks) with 64mb dedicated video max but if you put gaming 1st get the Dell 8600).
If you wait for the right discounts you should be able to bet that under $2,000. Order only 256mb 1 stick RAM from Dell and add your own 512mb PC2700 notebook RAM later yourself (in empty 2nd slot --only 2 slots in notebook) for under $100 when on sale -- example Kingston PC2700 512mb Notebook RAM I put in my notebook was 79.99 after rebates 2 weeks ago at Best buy.
What is a very good notebook for a Christmas gift? I wish to get one for my "gaming" wife. Iam willing to spend around $1500.00 -2000.00.