Well since no one else has answered your questions. The price is still undetermined. It will probably be comparable to what Windows XP runs retail, but noone can say for certain. A better deal might be to wait until they start shipping Windows Vista as OEM with new computers instead of building your own rig. There will be different editions so that will have to be factored in.
Video card/computer. I just recently purchased an AGP 4X Nvidia 6600 for my aging desktop. You will still have a better experience in gaming on a desktop PC then on a laptop, no matter what anyone says. If you are really into the best possible performance for desktop look at the GeForce 7800 series cards by nVidia. They also have
a list of "Vista Ready" cards (For desktop).
Vista Ready Laptops... Hmm.. I would say check out the Dell line of gaming laptops. (XPS) at
www.dell.com. There are people who swear by Dell and people who absolutely hate them. I bought an Insprion 700M laptop from them and its been a great machine - no problems here. The video card is pathetic on it but I didnt buy it for gaming. The only thing I personally recommend is avoiding doing any RAM upgrades via retail, since you can easily go to an online store like
crucial.com and install this yourself and save yourself a couple hundred dollars.. unless they have competitve memory prices
This of course is all my opinion so do what you have to do.