Buying enough DEDICATED video memory up front on notebooks is the most important factor in a notebook purchase these days. Supposedly a new technology is filtering down for better video quality without a separate card. But for right now you need 64mb dedicated or higher (128mb for gamers) to allow the notebook to function when needed for intense video applications.
No, you are pretty much stuck with your notebook video. If you can find out that your notebook had a higher dedicated memory option then you might be able to get one (but they are very expensive) and have it put in (it is soldered to the motherboard so this is not like changing out system RAM or hard drives, etc.).
No, you cannot just pop in any video card solution like on a desktop that has an open expansion slot. Not only do notebooks have space issues and heat issues they have a proprietary bios that will only accept certain devices.
If your notebook has a minipci slot (usually under the notebook) then you may be able to purchase and install a built in minipci card.
Nearly every notebook over $1000 today has a minipci card built in already however.
You can get a great notebook now for the $900-$1200 range that has more dedicated video and the 54G wi-fi built in.