Steve,
I have been using GPS commercially in Africa in my work for the last 13 years, and have used/owned quite a few, from numerous Garmins through to survey grade Trimble and Thales units. My own take on the use of GPS with a laptop is as follows:
1) To be honest I really don't trust systems that are as complex as lap-tops and usb/bluetooth connections or PDAs as navigational solutions... Why, well over the years I have had several laptops fail me, but a stand alone gps (i.e. recreational garmin type or similar) is generally designed to be put through a fair bit of punishment that a laptop cannot put up with. Most are at least dust and waterproof to a good degree. I have seen GPS units fail, but only after a minimum of one years DAILY use by a forest survey team... This is very demanding use.
2) A stand alone GPS is more flexible - car, foot, bike, boat you can take it along...
3) It is easier... Jump in, switch on gps, switch on car and go. As opposed to booting up, connecting cables and waiting for everything to be up and running. When you stop it is also easier to stuff gps in bag and leave vehicle. Esp if you are already the center of attention! I don't really want people seeing laptops etc in my car in built up areas for obvious reasons.

I do use a laptop connected to a gps for mapping use, and for that I have an old panasonic toughbook I bought 2nd hand. Tracks for Africa is fine, but (and this is just me) I am not a fan of all their "eco" statements and community GIS for Africa stuff on their site. No doubt their stuff is usefull, but on the other hand I dont want to only follow other peoples tracks and waypoints, and I certainly don't want to pay for it. I also have found that in the past I have over prepared, getting anal about maps and waypoints, and found out that a simple gps and map was enough.

But, in short I would say if connecting to a laptop then a simple GPS is enough, while still more than good enough on it's own - I have been quite impressed with the bottom of the range Garmin GPS 72: rugged, not too small, even floats!

If not connecting to a laptop then you might want a bit more features i.e. colour, better internal base map etc. If you don't mind trading portability out of the vehicle for a nice large screen then a 176 or similar would be ace!

For more of a compromise between portability and size the 60cs is good.

If you want small size then the vista is very good. I recently got a Vista Hcx and was VERY impressed with accuracy and ability to maintain gps position under heavy, wet tree cover. The high sensitivity chips now in use are a real step forward for gps! We were so impressed that we bought 14 to use for various purposes under thick rainforest canopy.

I have used all those and to be honest the vista is my current favourite - yes a tiny screen, but so portable and with a pretty decent base map. And anyway if I am lost I just pull over and try to figure it out, so the small screen is not that big a deal.

As for real time mapping software, I actually think the basic garmin world map for mapsource is not that bad. I have also used fugawi but more for it's ability to take scanned maps than any thing else. I am not anti-laptop, for sure on a trip like yours I would take one, but it would be tucked away somewhere safe, and the navigation would be on a stand alone gps and the music on the ipod.

So my final choice would be probably a 60 as a decent compromise between screen and portability, and if you want to hook it up, then you will have the cable, laptop and mapsource anyway. And some decent paper maps. I just think this is a more flexible, tougher option. All just my 2p.
Gil