Make sure the cover looks like this: 
http://i525.photobucket.com/albums/cc339/cascaderailroad/TrainzRailwayz.jpg
 
Trainz Railwayz Railroad Simulator TRS2006 build 3337. It has @15 TRS2006 routes, and @6 TC routes. You can download more additional routes from DLS, free.
 
This 2 disk CD requires no service pack upgrades whatsoever.
 
Mine was $14.95 at Best Buy. If you buy a prevously owned, second hand, opened, CD on E-Bay, it will not be re-registerable...and you will be unable to ever download off of the DLS. 
 
It has Paintshed, 
BUT can only paint @ 
20 choice Paintshed Template locomotives and cars, nothing else. 
 
If you have a Vista machine, you should have at least 1Gb ram, and 2Gb is reccomended...an upgraded Nividia video card or similar is reccomended. As with my GF Toshiba 1Gb Laptop with a factory video card Trainz is pretty choppy at times.
 
Most new laptops should play the game, unless you buy a very inexpensive, low end, inferior PC.
 
The reason 04 is great is, as when you create a route in 04, all users(04, 06, 09, 10) can upload your route.
 
As I am creating my route in 06...04 users will be left out in the cold.
http://i525.photobucket.com/albums/cc339/cascaderailroad/SnowDrift.jpg