I don't understand Vista, for the reason that, you shouldn't need to have a fast PC to run an OS that is there to run programs.
It uses more resources than it needs to, slowing even a reletively fast PC down.
The fact it slows older PC's down, unlike XP, shows how badly it can perform its task.
A Operating System should be light, so that programs run effective on it, with a machine that meets the specs of that program.
It shouldn't need to hog more RAM than XP, etc.
Its the old saying of "PC's get faster, so this doesn't really matter". But that isn't the point. A PC shouldn't have to be faster to run an OS, which is basically just a UI to access things quicker than you originally could before them.
I thought the whole point of having the UI done with Direct X for example, was to speed things up, not slow things down.
That is why I think Vista, even with its nice sparkly features, is useless.