If I understand your question correctly, you can make selections from different layers using the Select by Attribute tool. The process would be to use the Select by Attributes to make your first selection and once you get those results, go back into the Select by Attributes tool, change the Layer to the new layer you want to select from and change the Method to �??Add to current selection�?? (or one of the other options you may want to use, such as Remove from selected).
This allows you to have both of your query results displaying.
Is this what you were referring to?