Windows Vista has the indexing service. this indexing allows for you to quickly search for items via the Start Menu or any open explorer window. Windows XP didnt really have indexing till after Vista was introduced and they released the new Desktop Search Agent where indexing was then implemented with XP as well.
What I would do to save your hard drives is turn off the indexing service. Start>Run>Services.msc and there find indexing and disable it completely. Most people that know how to use a PC intensly know where their files are 99% of the time. There is a slight chance that you will ever have to use the Search Feature thus dont really have a need to have your files being indexed constantly. Turning off this service will cut down on the amount of disk activity that is going on.
Also another thing to check is things like Shadow copies. this is a service that automatically creates a backup of any document you are working on in case of a system failure where you would lose all the work done at that time, if you dont save every 5 minutes, or seconds like some of us, and not be able to recover the work already done. This service can also be disabled saving you some hard drive space in the process.