1. The first thing you want to do is open up your Registry Editor by clicking Start and then typing regedit in the Start Search box. Click enter to open this up.
2. If you are unfamiliar with the Registry Editor, it should look like this when opened up:
Now, you need to navigate to the setting where you can change Vista's default value.
4. To the right, the last setting you see should say WaitToKillServiceTimeout. Right click this and click Modify. Value Data is where you want to change this value.
5. What to change it to is the question. Vista has is set to 20000 by default which means 20 seconds. I wouldn't recommend setting this anywhere below 3000 and at the lowest, 2000. Right now, I have mine set at 3000, which is 3 seconds. You can experiment setting it lower at your own risk. If you have problems with Vista shutting down too fast, simply raise the time to a higher value.