If you are buying a new PC / Laptop for Vista you should bare the following in mind...
"A white paper published this morning by hardware analysis firm iSuppli, based on its studies of Microsoft Windows Vista running on multiple grades of computer hardware, has concluded that the software publisher's stated minimum requirements for the system -- which include an 800 MHz processor, 512 MB of RAM, and a 35 GB hard drive -- may not be nearly enough."
Source: BetaNews