Liz...
This is Sandy Sleuth's sister-in-law. I've been playing adventure games on a laptop for several years now, but I now have to purchase another laptop because the video card cannot be upgraded in laptops. Apparently, the video cards in laptops (at present) all come welded to the mother board as opposed to slotted...like in a desktop. As a result, you just can't update your video card as the graphics in the newer games require.
So...if you are going to go laptop, make sure you get a good one right up front, with a fast processor, plenty of RAM, CD/DVD drive, at least a 15 inch screen, and the best video card you can find with the most memory (currently 256 MB in the laptops I've seen.), and buy an external mouse as the one on the laptop is not good for gaming.
I got my first laptop at Dell. Got it with a docking station so I can use it with a mouse and keyboard (wireless). At the time it had the best video card available (Nvidia GeForce). But that video card has only 32MB RAM, so the newer games that require 64 and 128 MB video cards won't work. I contacted Dell about upgrading and they gave me the above explanation. I priced the newer laptops at Dell, then went to Best Buy and did a "build your own" using an HP program. Since the sales clerk at Best Buy was into gaming, he and I together designed my next laptop. And it was about $500 less than the Dell...which already was discounted $500. We also discussed upgrades and he had the same thoughts as Dell. So, if the capacity is out there, it's not well publicized.
I guess it all comes down to what else you will use the laptop for...which will necessitate the mobility. Desktops are infinitely less expensive and more upgradable. But they chain you to one room. I've gotten used to gaming on a laptop and I really enjoy the portability. So...my newest toy will be used strictly for gaming. And I hope the developers don't go beyond a 256 MB video requirement for a while!
Hope this helps.
JK