To print a particular record that you're seeing on the form you use a criteria for the command
DoCmd.OpenReport "MyReport", acPreview, , "[lngRecNo] = " & Me.txtRecNo
In the above example, the report opens to the record number equal to the record number you're viewing. For a subform to print, you need to put a subreport in your main report and make it's sourceobject equal to the same as the subform.
Michigan Dept. of Environmental Quality, Air Quality Division