As mentioned above, a scheduled task is what you're looking for. To run a script as a service read this:
Q4. How can I run my script as a service?
This is also a question with multiple answers, and none of them are the only way to do it. The first question to ask yourself is whether or not you wish to install the service on other computers besides your own.
A1. If you only wish to install the service on your own computer, The easiest way to do this is to use Pirmasoft RunAsSvc. This program makes services easy to install and easy to remove when necessary.
A2. If you wish to make the service available to anyone running your script, you can use SRVANY.EXE and ServiceControl.au3. You can then use this code to install your script as a service:
#include "ServiceControl.au3"
$servicename = "MyServiceName"
_CreateService("", $servicename, "My AutoIt Script", "C:\Path_to_srvany.exe", "LocalSystem", "", 0x110)
RegWrite("HKLM\SYSTEM\CurrentControlSet\Services\" & $servicename & "\Parameters", "Application", "REG_SZ", @ScriptFullPath)
or use the following code to delete this service:
#include "ServiceControl.au3"
$servicename = "MyServiceName"
_DeleteService("", $servicename)
There is one caveat to setting up AutoIt as a service. If the service is not installed using the above code, it must have the "allow service to interact with the desktop" setting or else automation functions such as Control* or Win* functions will not function. To assure the service does indeed have this setting, use the following code:
RegWrite("HKLM\SYSTEM\CurrentControlSet\Services[ServiceName]", "Type", "REG_DWORD", 0x110)
Taken from the FAQ topic on the AutoIt Forums. www.autoitscript.com/forum/index.php?showtopic=37289)