It's not a secret that Vista likes more memory and whoever has 2x1 GB now might want to migrate to 2x2GB before installing the OS. But, as we said before, you want to get 64 bit Vista in order to address all this memory.
DDR 2 667 will have to do with 2x 2GB but it will eventually migrate to DDR 2 800 MHz as you need to find big chips that can work at high speeds.
You will need over 2GB of memory because of multi, mega or giga tasking. If you launch a game in Vista you can burn up to 1.5 GB instantly and you don't need that much to spend the remaining memory. Once you use the whole 2GB, your super fast computer will start to swap memory around. So maybe you will want 4GB.
We know that the big boys such as Micron and Kingston already have 2GB modules available but these are currently super expensive. You can estimate that Corsair and OCZ will price its 2x2GB Vista kits for around $500-600 apiece. µ