I am very new at this but I have had this issue for quite some time. I have seen several posts on this and other sites in regards to Vista waking to run scheduled tasks and going back to sleep to soon leaving the tasks non-completed. If this has already been posted please accept my apology. Although I am not using the 64 bit version on Vista, your site has been very helpful to me, okay enough here goes. If the 2 min going back to sleep thing is/was happening to you this worked for me. I'm running Vista Ultimate 32 bit.
In the registry go to
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Power\PowerSettings
once there you will find a key 238C9FA8-0AAD-41ED-83F4-97BE242C8F20 expand this key, once expanded you will have another key 7bc4a2f9-d8fc-4469-b07b-33eb785aaca0, expand this key as well, expand DefaultPowerSchemeValues, once expanded there are three keys here each with a AC/DC setting, change all three either AC or DC or both which ever one you prefer, in decimal to the amount of seconds you want vista to wait to go back to sleep when awakened unattened. I have been using this for about a week so I hope helps someone else.
In the registry go to
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Power\PowerSettings
once there you will find a key 238C9FA8-0AAD-41ED-83F4-97BE242C8F20 expand this key, once expanded you will have another key 7bc4a2f9-d8fc-4469-b07b-33eb785aaca0, expand this key as well, expand DefaultPowerSchemeValues, once expanded there are three keys here each with a AC/DC setting, change all three either AC or DC or both which ever one you prefer, in decimal to the amount of seconds you want vista to wait to go back to sleep when awakened unattened. I have been using this for about a week so I hope helps someone else.