Most popular DB API sets on the Microsoft Windows platforms are ODBC, DAO and OLEDB, ADO. Windows OSes come with subsets (few drivers) of some of these APIs here is a little information what to expect:

DAO.Data Access Objects is not preinstalled on the most OS versions by default. Thus if you are trying to use it it is always better to pack your software with DAO redistributables. You can expect DAO installation on machines with MS Office (and especially MS Access), but in all other cases DAO is optional component or is not included.

ODBC. Rather old but universal it is available on most Win32 platforms by default. But on Windows 98 its default installation is not enough for the most components working through ODBC. Usually the user has some programs and other software that uses ODBC thus the ODBC is preferred choice for applications trying to run without DB redistributables. On the NT/2000 platforms ODBC is always available and can be used as long as the version or driver requirements of the software are not related to drivers and features not available in the oldest ODBC versions.

OLEDB and ADO. ADO is built over the OLEDB API thus in most cases these two APIs are packaged together. All Windows platforms starting with Windows 98 have them in their distributions but the components are optional. For the corporate applications ADO (or OLEDB sometimes) is the best choice and installation of the additional components is not a problem. For widely distributed applications this is different - ADO redistributables are good idea and checking code can be used to determine the available components.

There are many other universal or not DB APIs but all they are part of some product and always require redistributable files.