If i'm getting your question exactly you've an application in which you manipulate word and PPt files.
Well if that is the case you must be referring interop assemblies of these application and then the object model of respective application. The interop assembly you will find on your machine in most cases will be the matching version of the office installed. For example Office 2003 the version will be 11 and so on.
Microsoft claims that office applications are backward compatible so if you have office 2003's assembly, ideally it should work for higher versions 2007 & 2010. Certainly you won't get new features but you shouldn't have any problem for what you are targeting.
i've found a nice article http://devcity.net/Articles/163/1/article.aspx
Hope this will help.