We are spending a few days in Salzburg for the holidays and will be flying out from Paris after New Year's Eve.
We need advice on the following:
Should we take a train to Paris from Salzburg or should we rent a car and drive?
2. If we drive, can anyone suggest a stopping point in between to spend a couple of days?

Thats about a 9 hour drive and your drop off fees are probably going to be large. Since it sounds like you don't have a lot of time in between I would take the train and stop in Strasbourg, about midway. You can see some of the smaller Alsace towns that way if you like but Strasbourg will hold your interest for a few days on its own.

Transavia - a no-frills carrier owned by Air France / KLM - has twice-weekly nonstop service (Tue evening and Sat afternoon) from Brussels to Salzburg. Fare on January 6th would be EUR 60.48 per person all in, book ASAP as these will only go up!

Brussels airport is about 2 hours by train from the center of Paris via high speed Thalys service, change to the local at Bruxelles-Sud. You could spend a few days exploring Bruges/Ghent if you wanted to break the trip up.

www.transavia.com

http://www.b-rail.be/main/E/index.php
for train schedules in/to Belgium (cannot use for ticket purchase ex France due to ticket delivery restrictions)

http://www.thalys.com/fr/en/
to purchase your ticket from Paris to Belgium - select "Bruxelles-Midi/Brussel-Zuid ABS" if you are headed to the airport, ABS stands for "All Belgian Stations" and allows you to connect onwards from Brussels to any destination in Belgium. Cheapest fare for your journey is EUR 29.50 ("Smoove" fare), purchase as closely as possible to the beginning of the 90 day advance purchase window as they go fast. You should be able to print out your tickets at home. If this option is not available, you will need to collect them in France before travel at any SNCF station or boutique.

Hope this helps,
Andre

If you want to break the journey up, then Cologne/Koeln would be another great stopover option. You can reach the city by Thalys from Paris in 4 hours (see above for link) and there is daily service to Salzburg from there on TUIfly with prices in the same range as Transavia if you book FAST.

Hope this helps,
Andre

Oops - here's the link to TUIfly:
http://www.tuifly.com/en/index.html

I can't undersyand these suggestions about flying.

If you want to stop off somewhere, Cologne - six hours from Salzburg by train - sounds a good idea. Just get the train, changing at Munich: either a painless 20 minute change, or enough time to slip into town for a lookround and a few jars in a bierkeller

Let's see, flanneruk... 6hrs 34min minimum by train from Cologne main station to Salzburg (best connection I could find) for EUR 122.- vs. a 70min flight for about half the price... I certainly know what I would choose.

Hope this helps,
Andre

P.S. Cologne airport is a 15min ride by urban railroad (S-Bahn) from Cologne main station.