Vista will work beautifully on most new computers from now on. Intel / AMD both have great dual core chips which will be great for Vista, not to mention that most computers now come with 1GB of RAM.
If you upgraded from Windows 2000 to Windows XP and thought that was rough, you've seen nothing when going from XP to Vista. RAM......is essential. Check out most any review and you'll see how well today's faster chips, memory, and hard drive speeds all will play an important role for future Vista users.
Windows XP still allowed a lot of 98/2000/ME users to upgrade fairly easily and without a significant decrease in performance. Vista.......forget it.
Vista = new computer for me. Either Dual Core 2 or AMDs top chip, 2 or 4GB RAM, 512MB dual DVI video card, and top SATA speed for very large HD. The cool thing is that this can be had for less than $1,400.