Robert
This is by design.
The Disk Defragmenter in Vista has been changed to run as a Low Priority background process and as a Scheduled Task. This allows you to keep working while disk defragmenter is running without the need to worry about files being opened that could interfere with the defragmentation process or the system slowing down while you are working.
I recommend just letting it run on the default schedule, which is once a week.
If you want to see the current fragmentation report on the hard drive, you can see this from a command line.
Go to Start / All Programs / Accessories. Right click the 'Command Prompt' and select the 'Run As Administrator' option.
Type the following command.
defrag C: -a -v
Press Enter.
(This command assumes that C: is the system partition)
(This report could take a few minutes to complete)
This will show you a detailed analysis of the fragmentation on the hard drive.
