Ok, insert your own "switch back to XP" joke here. But seriously, if you are going to stick with Vista but want to wring as much performance as you can out of it, then take a look at this tweak guide by ExtremeTech. Don't expect any miracles, but here's what they have to say:
"Unlike previous Microsoft operating systems, Windows Vista is pretty streamlined right out of the box. It makes terrific use of a system's resources, but it's built as much for pretty looks and increased stability and security as it is for horsepower. It's time now for a course of action that will take the ball and chain off this baby and let it fly.
The ink on Windows Vista's EULA is barely dry, so it's very likely that more speed tips, registry hacks, and deep settings will be revealed in the weeks, months, and years to come. For now, here's our set of tweaks that can help you turn up the throttle on your new operating system."
Having tweaked a few OSes, including Windows 2000 and XP, here's a few tips for you to keep in mind:
Like ExtremeTech says, it's still early and we might see more performance down the road. Don't be discouraged if an hour of reading and tweaking doesn't make your system perform like you spent an extra $1000 on it.
Install everything you need to run your computer on a daily basis before tweaking. Before tweaking make sure everything works to your satisfaction. The next 2 steps will shed some light on why this is suggested, but ask yourself "how do I know if a tweak broke some aspect of a program if I never tested it before I started tweaking?"
Prior to making these changes make a good backup of your system and/or registry. Always have something to fall back on.
Take it slow. Don't try to make all the changes in one pass. Make a few changes, reboot, and see if everything works. Can you still print? Can you still run all the apps and games that you need and do all the basic functions that you do on everyday? If so, then move on. If not, take a look at what you changed and figure out which tweak broke it. Reverse that setting and try again. There is absolutely nothing worse than making 100 different changes, rebooting, and then trying to figure out why something that used to work doesn't work.
Don't stress if some of the tweaks are over your head. Some things are really easy to do, some things aren't. Tweaking a computer is not much different than painting, or working on car. Do what's comfortable with your level of knowledge. Some people would paint a bedroom door, or change a tire, but they'd never paint their house or rebuild a small block motor. Tweaking your computer is very similar, if there is something you're not comfortable in doing, don't do it. Or just try doing one change every day or so, and see how it works.