If you're looking for a cheap system that will work on a laptop then keep on reading!
I've just completed a round 2,500 mile trip off roading in the Italian Alps, driving down to Monte Carlo, and touring France. Before I set off, I did some research on connecting handheld GPS to my laptop.
When you plug the older Garmin units (I have a Vista Cx) into your laptop via USB, they do not relay their co-ords to a laptop. If your Garmin is a new version, and does relay positioning info to your laptop you can skip the next paragraph!!
There are 2 ways to get around this:
1) Garmin have created a free piece of software called 'Communicator' to overcome this problem. This only works on some handheld devices.
2) If your Garmin device is not supported by the 'Communicator' software you can buy a piece of software called Franson GPSgate. The software talks to the device, and brings back the co-ords. It costs about £35 pounds. The benefit of using GPS gate is that you can run multiple software at the same time, using the same GPS signal.
The solution I used
If you're looking for a cost effective solution, I bought a GPS dongle from Ebay for £20. I downloaded a free SatNav program callled MapFactor Navigator Free. It's a cracking bit of kit but the options take a bit of getting used to, so I would practice with it 1st.
The maps the program uses are from open streetmap, and are free. You just select the countries you want to download, and the program will download and install them for you. Because the maps are free you can keep them bang up to date. I updated mine a day before I left for Italy.
It is also well supported in showing you the nearest campsites, petrol stations, etc.
The only bit I couldn't work out (and I think this included with the pay version) is how to disable toll roads, but still plan a route via motorways.