You should be able to find pricing for these overnight trains at :http://ourworld.compuserve.com/homepages/euraide/overlist.htm
Prices listed are what you pay in addition if you have a railpass. Most of these trains will be 20 to 25 euros for a berth in a 6 bunk compartment and 25 to 35 for a berth in a 4 bunk compartment. Your trip from Salzburg might be slightly more expensive. Neither 4 bunk nor 6 bunk compartments will be as large (or comfortable in my experience) as you’re used to on Russian trains.

Thank you so much, oldlady, you have been a great help with everything. I’ve checked out the website and it really solved a few queries I have had for a long time. However, I saw that it doesn’t really coincide with the timetable that Eurail Provides for its customers. I downloaded a PDF file of complete eurail timetable, showing locations and time and duration of all cities covered by eurail, and for example, according the the PDF file provided by Eurail, there are no night trains from Geneva to Rome while in this euraide website there is. Or that I can travel on a night train from Venice to Salzburg while the schedule from the eurail website did not mention so. Maybe this euraide website was not updated recently? Or maybe it includes the timetables of locally operated trains?

Another question, I have asked in a forum elsewhere about night trains, and some of them commented that while sleperettes and couchettes and so forth are provided, some trains also offers seats, and most of the journey (especially in January-February, during off season) the train is not fully occupied, so you could stretch your leg a little, etc, making yourself more comfortable, is this true?

Could you describe how the seatings are in such trains? The ones in russia, they are divided into 12 or 13 wagons, up to 20 to 30, each wagons containing a small cabin or cubicle. These cubicle normally houses up to four people. Is this the case for eurail train too? Or are there only just seats, similiar to what you get in a bus?

Euraide may not be up to date, I’m not sure — train schedules seldom change. Euraide does not include all overnight trains. The Salzburg/Venice connection doesn’t show because Salzburg is not considered a major destination. That route may also require a connection and I think it arrives in Salzburg may be before 6:00 so it’s not technically an overnight train. At any rate, I would not use euraide for exact schedules. I’d check those at the station when I bought the reservations.

Russian train cars (wagons) are both taller and wider than those in Western Europe. In the west, some cars have compartments with 6 seats (3 facing 3) in 1st class, 8 in 2nd class. Others are just seats, no compartments, usually two seats on each side of an aisle. The fact that things are just bigger on Russian trains shows up in more comfortable sleeping compartments.

Oh, another question please? I know that eurailpass entitle us free boat/ferry rides across some lakes, like Thun and Geneva lake in Switzerland. Does it entitle us to discounts on rides to mountains though? Like I heard Swiss Rail entitle us to discount (only 40.90 euro) up Jungfrauch, while in Spiez, discount till 20 euro up Mount Pilatus. Does it hold true for EurailPass?

There are more bonuses available with a single country pass for Switzerland and with a Eurail pass. Bonuses sometimes change a little from year to year. Sometimes there are some requirements for bonuses — things like you have to book directly with the ferry company, not through an agent. A complete list of the current bonuses will come with your railpass.
You can look up the bonuses at www.railpass.com or www.raileurope.com Click on the specific pass and somewhere in the information will be a link for a complete list of bonuses. Raileurope is usually more up to date for information on bonuses, but the "info center" at railpass has better information for other issues/questions.

 
Remember that the Eurail leaflet is not a comprehensive timetable. It’s a summary of the most important connections between main cities in Europe which could have interest for tourists, and covers maybe 5 or 10% of all train connections in Europe. No small stations are shown, no regional trains are shown, just the important trains between major cities, but all the other trains are free as well. There is no such thing as a special “Eurail network” or a “Eurail train”. All trains run by the state train companies of the&nbsparticipating countries are free with the Eurail pass (with a few exceptions). Deutsche Bahns homepage is quite comprehensive and covers most trains in Europe.
 
There is a night train from Geneva to Rome. It is train EN311/313, leaves Geneva at 21.36 and arrives in Rome at 9.12.

Chrismo is correct: the best place to look up schedules is the German rail website, the English page is: http://reiseauskunft…
Last time I downloaded from there, you downloaded the entire schedule between two stations as opposed to an abbreviated schedule between a number of major cities.

For a route with several direct trains or trains with one connection the German rail website will not show all the possibilities of local and regional trains with a “standard search.”  Use the pull down to search “without ICE” or “without ICE/IC/EC” for more options.