As for the Runtime Version, Excel 2000, Excel 2003 or Excel 2007 or later, are compatible. So install it according to the Excel version on the local PC.
The Development Version is compatible with Excel 2003 and later versions. *Note: If you have PCs which use Excel 2000 or Excel 2003 in your system, save the Excel workbooks as the 2003 format (*.xls), when they will be used as Front End Forms, or commonly shared or distributed Workbook. This is because files saved in Excel 2007 Workbook format (*.xlsx) may not be opened in Excel 2000 or Excel 2003.
The database itself is mandatory for dbSheetClient, and dbSheetClient requires either SQL Server 2005/2008 or Oracle 9i/10g/11g to be installed as the system database.
If your database is working on one of the above, dbSheetClient can join the use of database. In other words, your database can be used as both the user database and the dbSheetClient database.