Some problems about word operation

Question

I am trying to use c# doing some operatin with *.doc files. But here are the problems i encountered: 1.There is already an item"Microsoft Word9.0 Object Library " in the COM reference tab. After i installed the XPpia ,there should be a new item "Microsoft Word 10.0 Object Library ",but there was not. I use Office 2000.So what 's the problem? What 's the difference if i install pia or not? Does PIA only fit office xp? 2. I downloaded a program from this website,and run it ,the same error came up as before. the error line is:aDoc.Application.Documents.Open(ref fn, ref miss, ref miss, ref miss.... and error infor:System.InvalidCastException,QueryInterface failure I think maybe the environment setting of my computer.So can anybody tell me how to deal with these problems.Thanks