In defense of UAC, Dr. Jesper Johansson, co-author of Windows Vista Security (Securing Vista Against Malicious Attacks), has written an excellent article. If you want to gain a better understanding of UAC, its intended purpose, and how to use it, read The Long-Term Impact of User Account Control.
It is possible to edit the configuration or disable UAC using Group Policy for systems in a network domain, or by using the Local Security Policy settings for standalone systems. However, Microsoft does not include the ability to access these settings from Windows Vista Home or Windows Vista Home Premium. Users of the Windows Vista Home operating systems have to manually edit the Registry to change the UAC settings.
Let me preface by stating that I do not recommend disabling UAC. Johansson's article clearly explains the benefits of UAC, and for the vast majority of home users, leaving the default UAC configuration is advised. If you are a more advanced user, or you just really feel a need to change the UAC configuration though, just follow these steps:
Click Start, then click Run