According to GP Installation Instruction, To set up an ODBC data source, enter the name you assigned to the SQL Server when you installed Microsoft SQL Server. A data source name called Dynamics GP also is created using SQL Native Client. If you don’t want to set up an ODBC data source, mark the Do not create a data source option.

In case, you are stranded when your ODBC DSN is not listed in GP’s Welcome Screen Server Dropdown, on a 64 Bit System, rest assured that you have not created DSN on the correct DSN Maintenance wizard.

More info…read my collegue’s (Vaidy Mohan) blog….this will help you http://www.vaidy-dyngp.com/