The best and safest thing to do is not to disable UAC entirely, but to disable the elevation prompts using the freeware program TweakUAC
. In doing so, you'll still benefit from certain features of UAC such as Internet Explorer operating in protected mode and programs not running with administrative privileges by default.
is a free standalone program which doesn't run in the background. Simply run it and select from three options: Turn UAC off, Switch UAC to quiet mode and Turn UAC on. Switching UAC to quiet mode will leave UAC on, but disable the annoying elevation prompts.