In Aust, we have RNAV approach, (which are also called GNSS) and GPS arrival. Your question says GPS approach, which does not exist.
do you mean GPS arrival? (described below)
or do you mean GNSS aproach? (described in previous post-see also RNAV approach!)
(This bit above added, as I may have misread the question)
It might depend a bit on where you are. i was under the impression that in Australia, there are still GPS arrival which are VERY different to an RNAV approach, unless this has changed in the last 12 months.
The RNAV description as above is accurate as a runway approach, the 'RNAV arrival' sounds like what we could call a 'STAR' (Standard arrival route), which (as described) would take you to the IAF of an instrument arrival (which may be an ILS, RNAV, VOR or NDB approach).
a GPS arrival (in Aust) is mostly the same as a DME arrival, in that the GPS must be tuned to the lat and long of a vor/ndb, and the pilot descends based on distance from that navigation aid. Usually the gps arrival is broken into sectors, with different steps (ie distances at which you can descend) depending on where the aircraft is coming from.
The biggest differenc, is that with an RNAV, pilot is following a 'line in the sky' (usually aligned with a runway), and should be on a constant profile (such as with an ILS).
With a Gps arrival, the pilot can manouver prior to crossing the FAF (final approach fix), and may not be runway aligned- a much less precise approach, but useful as they can be used to get below cloud without going significantly off track (if at all). Though in Really bad weather, an RNAV would be preferred for it usually has a lower minima.
Clear as Mud?