The 430 doesn't have a DME receiver, but GPS distance is a legal substitute. To determine the GPS distance, do a direct-to to the destination airport, hit the PROC button to select an approach. If it's a precision approach, it'll automagically load the ILS freq into the standby position and the distance to the MAP will be on the active flight plan page.
If you haven't, read the manual; the 430 is an impressive piece of gear but most people learn only the bare minimum to use it. Dig a little, download the simulator program from Garmin's website and wring it out.