Performance Point is a SharePoint feature, not a SQL Server one (also not from SSRS), so I believe Entrerprise is not needed. (can't find documentation though that backs this up).
You might want to check the edition of SharePoint though, you might need Enterprise there.
ps: there's no SQL 2008 BI editon. The BI edition was introduced with SQL Server 2012.
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MCSE Business Intelligence - Microsoft Data Platform MVP