In the older versions of Windows like XP / 2000, to turn a feature OFF you had to Uninstall it completely from your computer. But in Windows Vista the features remain stored on your hard disk, so you can turn them back ON if you want to. Turning off a feature does not uninstall the feature, and it does not reduce the amount of hard disk space used by Windows features.You can access this very cool utility via Control Panel, Uninstall or Change a Program, and in the left hand side menu, "Turn Windows features on or off". You will get an UAC prompt and that's about it [Screenshot Below - Click to Enlarge].
From this cool interface you can switch ON / OFF some popular services like the Microsoft Message Queue Server, Print Services, Remote Differential Compression, ActiveX Installer Service, to the Games, to the Indexing Service, Internet Information Service, Microsoft .NET Framework 3.0, Removable Storage Management, RIP Listener, Simple TCPIP Services, SNP Feature, Windows DFS Replications Service, Windows Fax and Scan, Tablet PC Optional Components, Telnet Client, Telnet Server, TFTP Client, Windows Meeting Place and Windows Process Activation Service.
Also, you maybe interested to know List of Services that you don't need in Windows Vista to make it work faster.