The majority of the roads in Laos are dirt roads and while some of the dirt roads are very good, others are less good and often change to mud in the rainy season. Don't know what version of the Laos map you got but look at the Legend of the map and you will see that most of the roads, even though shown as a line, are in fact dirt.
Have also look at some of the trip reports (mainly motorbike so their may be areas which are single track and noy suitable for a 4WD) like
http://www.gt-rider.com/thailand-motorc ... t5702.html (done just at the start of the rainy season),
http://www.gt-rider.com/thailand-motorc ... t5213.html (a trip to the north of Laos) or this one
http://www.gt-rider.com/thailand-motorc ... t4640.html (a 9 day run from Vientiane but this can be shorter as well).
A good source of information for road conditions, places to see, eat and sleep in Laos is Jim-Oi. You can contact him at
http://www.remoteasia.com/contact.html.
Best time to go is after the rainy season at the end of the year (November/December) or early in the year as then the forests are still green and the rivers have subsided a bit.
Please be aware that, in case you rent a vehicle in Chiangmai, you will need permission from the owner of the vehicle to bring it to Laos as otherwise customs/immigration won't let you cross the border.
Anyway, as you mention that you have 10 days, I would recommend that you start directly from Vientiane. Jim-Oi can also help with vehicle rental, etc.
"There's always something waiting at the end of the road, if you aren't willing to see what it is, you probably shouldn't be out there in the first place."
