I'm using a five year old Magellan 400 w/power-data module hooked to an
HP Pavilion laptop running Microsoft Streets and trips 2003.  I have the
external antenna for this Magellan burt have never hooked it up, the
bare unit picks up just fine.
I would like to comment on the trip planning/tracking software
available.  I have not ried to use the Topo USA files from Delorme, I'm
rarely off-road and don't really need the topo information.  But I have
tried all three of the most popular programs.  Microsoft Streets and
Trips is far, far better at trip planning than any of the others based
on my use and comparison.  The biggest difference I found was in finding
obscure street addresses.  I have used Streets and Trips to plan, in
detail, six different trips, each in the 1,000 to 3,000 mile range and
the only complaint I've had is that it sometimes does not give me the
exact exit number to take when leaving the freeway.  I have a friend
that lives inside a gated community in So Cal. ONLY Streets and Trips
can find her address.  The other programs don't even show the roads, let
alone have the address indexed.  Streets and Trips has also done a good
job of finding campgrounds or RV parks for me.
Just my opinion, YMMV.