Why would this be an unrelated table? If you are passing a vlaue from the current table as a key for the lookup, why not define a relationship based on the field storing that value?
It is also possible to use set variable to copy the value from the table's field into a variable, switch to a layout based on the other table and use it to perform a find. Set variable can then be used to bring a value thus looked up back to the original layout and it's table.
But why go to all that trouble just to avoid defining a relationship to the look up table?