Railroad Tycoon 1.06

[pakrat2k2]

on steam forum.... user posted how to get it to work

The 1.06 patch won't install over the steam version, because it uses a different .exe (one that doesn't check for a cd)
If you reinstall the official 1.05 patch over the steam version, the 1.06 patch will install but the game will ask you to insert a cd.

You should be able to fix this by getting the 1.05 cracked exe and installing the 1.06 patch over it. The game should run fine that way.
But before you do that, check if it's legal where you live. In some countries it's illegal to crack a game even if you own it.