you are out of luck as far as Microsoft Office is concerned. This is the price you pay when you buy a system without all of the disks. Actually, your copy may have been illegal if the previous owner kept the disk and installed it on another machine.
No, you cannot copy the Office files from another machine -- they must be installed so that the registry is properly configured, and that requires the Office CD. To use another's CD, or in any way install their copy of Office on your machine would be piracy.
But there is an out -- download and install Open Office. It is an open source suite with most of the the features of Microsoft Office, and it is free. Some users feel that it is generally superior to the Microsoft package.
Back to lessons to be learned: Besides insisting on all appropiate disks when purchasing a used system, another act might have saved you this problem. Had you made a Ghost or Acronis image of the entire disk onto a bootable CD, you might have been able to reinstall your entire system, including MS Office.
Hope this helps
Frank
Recently, I've fiddling around my computer, and I guess I deleted something that made my computer not be able to run Windows XP Pro. So I had to use my recovery CDs (Windows XP Home) in order to set everything back up again. Of course I lost all my software, including Microsoft Office 2003. I bought this computer at Ebay, and all the software including the OS was already included in the computer, but I had no XP Pro CD, or Office 2003 CD. I can live with Microsoft Home, but the thing is, how do I restore the Microsoft Office that I had all along? Obviously it's gone to oblivion, so right now I'm trying to get all the Office files from another computer, and trying to get it onto my computer. But the thing is, I don't know how to install this thing. Is there an install package somewhere in the harddrive? I've been trying to find it on another computer, but I can't find it. No way would I want to pay money to get Office, but right now I'm pretty desperate in trying to find a copy so I can do my school work. If anybody could give me advice, that would be great. Thanks!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic