you should avoid using Vista on older hardware, especially single core systems when it comes to Vista. I installed Vista Basic on a laptop with a single proc and 1 gb ram. I dumped it due to performance issues (and the fact my friends and I am dumping windows from our home environments).
The Vista ready sticker scam is really coming to light in recent litigation against M$. Systems that meet the "minimum" requirement had such bad performance that you had to go back. This happens a lot in game software where the minimum requirements can be met with just about any $500 computer built in the last two years but they use the game to benchmark the performance $3000 computers.
If the previous post about the memory requirement is referring to computers about to be purchased then the processors will almost always be a dual core model.
2 GB will work fine in Vista and should be considered the minimum in all Vista installations. The biggest determinate of performance in my opinion is the use of integrated (shared memory) or discrete graphics (dedicated with shared memory to). Integrated graphics just suck with Aero in Vista.
Vista really belongs on the $1000 or higher computer market since these are the computers with dedicated graphics. You can easily add the cards in desktops, just purchase the lower end versions due to power supply requirements. Notebooks however are stuck with what ever they have from the factory.
