We aren't talking notebooks, but netbooks a 'small' difference (excuse the pun), Vista simply won't run unless crippled or like treacle, on the likes of an Asus EePC 901 or MSI Wind, etc. with an with a 1.6 GHz Intel Atom processor and 1GB of RAM.
That is why they were being offered for sale with either XP or Linux as the OS since Vista is a resource hog.