powercfg.exe works a little differently in Vista, and the "presentation" profile isn't included by default (at least on my machine. so you can setup a "presentation" profile and then use the following to get the GUID
powercfg.exe -list
and the following to set it to that GUID:
powercfg.exe -setactive GUID
Alternatively, you can use powercfg.exe with the -change or -X to change specific parameters on the current power scheme.
Snippet from "powercfg.exe /?":
-CHANGE, -X Modifies a setting value in the current power scheme.
Usage: POWERCFG -X <SETTING> <VALUE>
<SETTING> Specifies one of the following options:
-monitor-timeout-ac <minutes>
-monitor-timeout-dc <minutes>
-disk-timeout-ac <minutes>
-disk-timeout-dc <minutes>
-standby-timeout-ac <minutes>
-standby-timeout-dc <minutes>
-hibernate-timeout-ac <minutes>
-hibernate-timeout-dc <minutes>
Example:
POWERCFG -Change -monitor-timeout-ac 5
This would set the monitor idle timeout value to 5 minutes
when on AC power.