Deane,
If you want anything that will handle Trainz as well as 3d modeling, you need a gaming machine such as the DELL XPS-series or their flagship Alienware machines. Their Precision Mobile Workstation series are similar spec'ed as the XPS-series, but have the mobile Quadro which do not play games very well, and will sadly have poor performance. The other thing I've noticed too with the Quadro cards used by DELL is they are the lesser quality, or as I should say, older chipsets. This makes a big difference in the performance as well.
When I was pricing out a gaming laptop, I ended up with the Alienware M17x. At the time the XPS weren't up to the same performance level as the Alienware machines. This has changed, but keep this in mind that the XPS are the cheaper gaming machines. They are great in their own right, and probably capable of running Trainz, but they don't have the aluminum case that the Alienware machines have. This makes a big difference when it comes to cooling. The aluminum will help dissipate the heat much better than the plastic.
So in the end, I ended up with the M17x which is about two years old now. It runs Trainz Ts12 full throttle and the graphics are nice. The machine has a discrete ATI graphics card. The latest M17x has the NVidia card installed.
Now this machine is awesome, but as it's heavy! I regret getting it for that reason because my hopes were to take the machine with me when I traveled. I have to use two hands to life the bag or limp with it because it's so heavy. The other issue too is the battery is paltry and will run out in an instant without power. It eats batteries like a cold drink does ice cubes in the hot sun so I have to keep the machine plugged in when using games such as Trainz, SimCity (SC4), and others.
Bill is right. You need a cooling pad. This is another addition to my carrying bag. That machine is more than a lap warmer. It will figuratively roast the chestnuts!
John