TweakUI is a popular system configuration utility made by Microsoft since late Windows 95, and it provides quick and easy access to configure certain features in Windows without resorting to reshacking, registry editing, or other more dangerous tactics. Its not the most brilliant piece of code ever created, but its a nifty tool to have. You can download it for Windows XP/2k3 x64 and x86.
To get TweakUI working on Windows Vista, just download the XP version with the correct architecture (i.e. if you have Vista x64 download TweakUI x64, and if you have Vista x86 download the x86 edition). After setup is finished, right click the shortcut to TweakUI -> Properties -> Compatibility. Set it to run as an administrator and in XP compatibility mode. Close the dialog and run the app.
Most of the tweaks available in TweakUI are also there in Totalidea Softwares TweakVI utility.
It does most of the stuff TweakUI can do, plus a lot more Vista-only tricks; the basic version of TweakVI is free. Between TweakVI and TweakUI you should be able to do everything you ever wanted to and then some. And of course, if you need to tweak the hell out of the Vista bootloader, you are new best friend is none other than our very own EasyBCD. With all these tools, there is no excuse to ever settle for less than perfect. Happy hacking!