If you want to mess with the shut down time, then you have to know that will actually chance the time Windows takes to shut down all services. This option is well hidden into registry.
Type in regedit and follow the path below:
Here you see plenty of field in the right part of the screen. Just let them be, we are only interested in the last one in order to ameliorate this problem. Under the column Data, you see the time it takes to shut down a service, it's about 20 seconds. Double clicking there will allow you to chance the value. Make it anything between 20000 and 5000, as setting it below 5000 will cause windows to crush often when many services are in progress.
Now, this should make your windows Vista shut down process a bit faster. If you like this tutorial, feel free to read my other tutorials.