convert the spreadsheet to Office 2003 or lower (i.e., insert the excel 2003 spreadsheet into ArcMap as an object on a computer that has Office 2003 installed) or copy and paste the cells from the spreadsheet (as long as you do not use raster fonts).This workaround does not work unless Office 2003 is installed on the machine. Knowledge Base article 29569 contains more information on this topic: <a href="http://support.esri.com/index.cfm?fa=knowledgebase.techArticles.articleShow&d=29569" target="_blank">http://support.esri.com/index.cfm?fa=knowledgebase.techArticles.articleShow&d=29569</a>