If you wish to run Windows Vista and buying a laptop right now? What would you need?
Here is a readup. But make sure to look for Premium Configuration as otherwise, you will not be able to run the new "GUI" from Microsoft. Whoever said that you don't need more hardware to run a new Microsoft OS must be turning in his grave. Microsoft has always proved that their new OS will need more ram and more processing power then ever. Now it also needs more hardware resources. Read more about it here.
I would stick to XP and if I need to swtich, will switch to Mac or Linux. MacOS can give a similar or better GUI now and a cheaper configuration too.