I'm a little new to track making, but I have come across some good sites that have helped me be not as lost....
First checkout MTMG's Track Building Tutorial:
http://mtm2.com/%7Emtmg/traxx/
Then checkout Binedit, a program to analyze the models used in MTM2 here:
http://www.mtm2.com/~binedit/
Tutorial:
http://mtm2.com/%7Ed2s/binedit/
Anyway, all the models, i.e. the ramps, and the dirt are made of textures in the RAW format. You can easily pull apart a stock track using WinPod to edit the textures:
http://mtm2.com/%7Emtmg/downloads/mtm2/mdmre/Winpod.zip
After extracting the files you can convert the raw files to bitmaps for editing, here:
http://mtm2.com/7Emtmg/downloads/mtm2/g ... RawGui.zip
You can now edit the textures, convert them back using FlyRawGui then creating the new pod using Winpod.
Good luck!