Two interesting entries on Microsoft's Vista Team blog shed some more light on the hardware configuration you'll need to get the best performance out of Windows Vista.
First, check out the specs on this custom PC made by Microsoft and Dell to mark the shipment of Vista:
Intel Core 2 Duo E6700 Processor
512MB NVIDIA GeForce 7900 GTX
4GB RAM Dual Channel DDR2 SDRAM @ 667mhz
1Terabyte RAID0 SATA HDDs (2x500MB) Update: a reader pointed out that this should probably read 2x500GB.
48x Combo + 16x DVD+/-RW Double Layer Burner
Dual TV Tuners (Analog)
Dell 30" Widescreen Flat Panel Monitor
Full 5.1 Surround Sound
That machine gets a 5.2, the highest rating on Microsoft's index of computer performance. Comparable configurations on Dell's Web site are priced upwards of $4,600.
Here's a post from Windows chief Jim Allchin describing the ReadyBoost feature that allows users to squeeze better performance out of a Vista machine by plugging in a USB flash memory drive with at least 230 megabytes of memory. Allchin notes that this feature will be particularly helpful for computers with 1 gigabyte of memory or less:
When comparing the performance of Windows XP and Windows Vista on a PC with 1 GB of main memory, Windows Vista is generally comparable to Windows XP or faster. However, we also know that in some cases, on PCs with 512 MB of main memory, applications on Windows XP may seem more responsive. Why? Mostly because the features in Windows Vista use a bit more memory to do the things that make it so cool, like indexing your data, keeping the fancier AERO UI running using the desktop window manager (DWM), etc. The less memory in your machine, the more often the OS must randomly access the disk. This slows system (performance) in cases where your applications just barely fit in memory on Windows XP but not quite in Windows Vista.