TOO MUCH ACTIVITY IN VISTA
Vista had the bad reputation of trashing or doing seeks and writes to the Hard Drive very often.
One of the reason this happened is because in Vista, the History for all the Schedule Applications was turn on, hence the computer doing more work while idle.
There are many Schedule Tasks on both Vista and Win 7 - However in Win 7 several have been turn off as they were not really needed - I know because I was a beta tester for Win 7.
In addition, the History for all those Task has been disable. But the System Schedule Task remain for the purpose of maintaining the Operating System in order and for accumulating Error messages that are sent back to Microsoft.
The situation was much worst in Vista and you have to remember that the System Schedule Task, WILL STOP as soon as you Boot and begin using your computer. They are set to Stop so that your system does not slow down, but as soon as the computer has been idle (no mouse movement or anything else) those task begin to process themselves, if the idle stage stops, so does the Task.
If you want to see the System Schedule Task, go to the Start Menu, type Administrative Tools and from there you can choose Task Scheduler --- NOTE - Please do not turn off any of them off if you are not sure what you are doing or if you do, you can always go back and turn them back on.
The indexing on both Vista and Win 7 works the same way, they stop when idle time stops and continue when idle time begins. But in Win 7, as a test - boot the computer and wait about 10 minutes tracking the hard drive activity light. You will noticed that it begins to slow down until it stops.
There are also System idle processess running in the background, these processess will stop while the computer is use and stop. This is also another issue that has been fixed better in Win 7. Processess are communicating back and forth with other componenets of the computer hence, you will see the light turn on for a few seconds here and there - even during non idle times.
Lastly, connecting to a NAS - an external hardware, or even your router, will make the hard drive light flash a few times. These communications can't be stopped as the computer needs to be ready for you when you begin to use it again. To a router because it needs to maintain protocol communication with it, to a NAS because the computer may be doing incremental or full back ups, or staying connected with the hardware on a NAS.
But my final point is that Win 7 is much better at terminating those background task if there is no change once it has finish checking. so Disk Trashing in Win 7 is not at all bad.
If you can upgrade to Win 7, but do a clean install - depending on how you have your computer connected, the Trashing won't be as bad. The reality is that the words - Disk Trashing - came to be use more often with Vista, but it's an incorrect term. Simply because Operating Systems work in the background as well specially when idle.
Sorry for any spelling errors, but i hope this gives you a better understanding of what happens behind the scennes and that Win 7 is much, much, much better at handlng the idle procesess.