Using sendandload to populate a readonly textfield?

What i am after is the following:
1 user fills in a form
2 one of the fields represents xCoord and yCoord
3 both fields are readonly and can be filled in by pressing a link which pops-up the flash file.
4 Click on the flash map, will send a xCoordinate and y coordinate to the form
5 user sees the values of the coordinates in the readonly textfield
6 if the user is satisfied he submits the form.

The as code and php file works correct when i save the coord vars directly in a mysql db. But i want to show them first in the form textfields???

Using php and i tried

        <td><input name="xCoord" type="text" id="xCoord" readonly value="<?php echo $_REQUEST['xCoord']; ?>" size="5" /></td>

Any advice??