Depending on your date settings:
SELECT Project, CurrentDate, DMax("CurrentDate","YourTable","Project=" & [Project] & " AND CurrentDate<#" & [CurrentDate] & "#") AS PreviousDate FROM YourTable
OR
SELECT Project, CurrentDate, DMax("CurrentDate","YourTable","Project=" & [Project] & " AND CurrentDate<#" & Format([CurrentDate],'mm/dd/yyyy') & "#") AS PreviousDate FROM YourTable;
Note that a renamed Date to CurrentDate. Date is a reserved word. Better not use it as a field name.