UINT __stdcall AppendComboBox(MSIHANDLE hInstall) {
 MSIHANDLE hView, hDatabase;
 PMSIHANDLE hRec;
 int HowManyRecs = 17, StartRecIndex = 4;
 char valuebuffer[20];
 char *valbufptr = valuebuffer;
 hDatabase = MsiGetActiveDatabase(hInstall);
 MsiDatabaseOpenView(hDatabase, "SELECT * FROM ComboBox", &hView);
 // Now append 17 records.
 for (int i=0; i < HowManyRecs; i++) {
  hRec = MsiCreateRecord(4);
  MsiRecordSetString(hRec, 1, "COMBO"); // Column1: Property tied to the entry
  MsiRecordSetInteger(hRec, 2, StartRecIndex+i);
  // Column2: Display order of item
  MsiRecordSetString(hRec, 3, _itoa(StartRecIndex+i, valbufptr, 10));
  // Column3: Value to set property to
  MsiRecordSetString(hRec, 4, _itoa(StartRecIndex+i, valbufptr, 10));
  // Column4: Display text for item
  MsiViewModify(hView, MSIMODIFY_INSERT_TEMPORARY, hRec);
 }
 MsiViewClose(hView);
 return ERROR_SUCCESS;
}

VBScript can also be used in place of the code above. This code would then be launched via a VBScript custom action. If you would like to use VBScript, you need to use the MSI Installer Object. Sample code using this object is installed with the Windows Installer SDK.