Problem referencing Office 2003 Library

Hi Experts,
 
    I wrote an application in C#  that opens an Excel file, does some things, and then closes it.  I originally wrote the program to use Office XP, and it worked great.  Now my company has upgraded Office from XP to 2003, and now I can even compile my code.  I get: "The type or namespace name 'Excel' could not be found (are you missing a using directive or an assembly reference?)"  I deleted the reference to the old Excel Library, added a reference to the new one.  It still doesn't work.  Here's a little sample code of what I am trying to do:

using Excel;       //<- I get my error on this line and every line that references Excel after this.

Public Class Test
{
     Excel.Application excel;
}

Any help would be great...

Thanks,
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