如何从SSIS Excel文件名解析日期

I want to use the foreach container to iterate through a folder matching something like: "Filename_MMYYYY.xls". That's easy enough to do; but I can't seem to find a way to parse the MMYYYY from the filename and add it to a variable (or something) that i can use as a lookup field for my DimDate table. It seems possible with a flat file data source, but not an excel connection. I'm using Visual Studio 2005. Please help!I want to use the foreach container to iterate