Well, first off, it's not going to show TM anywhere, since it's not an official game by anyone (You do know TM was created by members here, right?
Second, RT3 is such an old game it's not going to show up in that list.
The read me that came with the cd version of RT3 does list the System Requirements.SYSTEM REQUIREMENTS
OS: Windows 98/ME/2000/XP
CPU: 400 MHz
RAM: 128 MB
Video Card: 16 MB 3D
Disk Space: 1.2 GB
Other: 4X CD-ROM, Mouse and Keyboard, DirectX compatible Sound card
with speakers/headphones recommended
Railroad Tycoon 3 has been successfully tested with the following video card chipsets/families:
NVidia: GeForce (all versions), TNT 1 and 2, NForce
ATI: Radeon (all versions), Rage 128, Rage Pro, Rage Fury Maxx
Intel: 810, 845, 865 (a.k.a. 'Intel Extreme' and 'Intel 3D Direct' graphics)
S3: ProSavage, S4 Savage, Savage 2000 (See Troubleshooting – 5 I)
Matrox: Parhelia, G400/450/550
PowerVR: Kyro I and II
3DFX: Voodoo 3, Banshee, Voodoo 5 5500 (See Troubleshooting – 5 H)
3Dlabs: Oxygen VX1/Glint R3
Trident: Blade T16
Note: Even if your chipset is not on the above list, it should work, provided you have current drivers (Direct X 8.1 or above) for it.