Hi, In addition to Doug's usual excellent thoughts, I would put forward the following for your consideration.
1 A basic reformat and fresh install of Windows will take less than 45 minutes or so.
2 You will need to install your applications so will need to have the executables backed up safely to removable media ( with all other important stuff!) and your other installation CD's handy
3 You will have some updates to do… and maybe some drivers to install but it shouldn't take too long…
Once you have done this,the machines will seem to fly…. freed from all the accumulated junk that seems to gather over time and slow things down; they will be sleek, lean, fast and fit again,and you can relax knowing that they are now virus free and any undesirable code has gone.
If the Product serial keys are likely difficult for you to find, then I advise that firstly you check that the licensing position is absolutely correct and that you are entitled to use the applications in the way you intend.
This is important as it would be quite wrong to use/install any application that was incorrectly or not licensed.
Once you have checked the licensing position and you are sure you are fully legal then take a look here:
http://www.belarc.com/free_download.html
If these are personal machines and not business then download and install the application…give it time to run it will seem to stall for a short time when running, but just give it a few minutes…it will then tell you all you ever wanted to know (and probably a lot more!) about the computer and its applications etc.
It wil also show you the licence keys that have been installed for Office etc.
If these machines are to be used for business, there are other audit type applications that will also tell you the serial numbers that have been loaded in your machine as Belarc will not normally be appropriate in these circumstances. (see their notes on licensing)
Post back and let us know how you go
Regards
paws