What you have is an Operating System, (OS), called Windows XP Home. There is another OS in the same family called Windows XP Professional. It has slightly more features.
Microsoft Office is a 'suite' of applications, which can include Microsoft Word, Microsoft Excel, Microsoft Access, Microsoft PowerPoint, Microsoft FrontPage, and Microsoft Outlook. There are various versions of Microsoft Office, the latest being Microsoft Office 2007. I personally have Microsoft Office XP, (2002), but I don't have all the separate applications. I don't have Microsoft Access, PowerPoint, or FrontPage. That was my choice when I purchased Office with my computer.
I cant tell you what, if any, Microsoft Office applications are available on the XP CD you have. If the computer is a DELL, then it will have a Service Tag code somewhere on the case, or in the documentation that came with the computer, and if you visit the Dell.com web site and input that Service Tag code, you may be able to see the specifications of that computer, and that may show you what applications the computer was originally installed with. But, generally, Microsoft Office applications were included on a separate disk to the CD that included XP. My DELL computer is like that.
If you are satisfied that neither the computer as it stands now, nor the CD's that you have, include Microsoft Office, then you will have to purchase the Office suite of applications yourself. Any good PC store where you live will have the Office bundle, but as Office comes in many flavors you will need to look carefully that the one you decide to buy has all the separate Office applications you require.
There will be many web sites where you can also purchase Microsoft Office. Amazon will be a very good resource. But again, check carefully what is included in the Office suite before you hand over any money.
Good luck, and I hope that helps.