This is how I got it working.
1. Download the source code.. http://www.mediafire.com/download/acxxvm29r7dp49w/ttisource-theExperiment.zip
or https://mega.co.nz/#!JIlDwRKI!xXPtNur5czI9jRUSLN_xKyrcDZkboPmTIpgo1ehftcs
2. Extract it into your C: drive, don't extract it anywhere else
3. Once that's done, open the folder, run and install python 2.7 (it's in the folder)
4. Once you have installed it, run Increase TCP Buffer Size.bat AS ADMINISTRATOR and reboot/restart your computer
5. When that's done, run and install vns.full (it's in the folder)
You probably don't want to join the club, so uncheck the second box, but you have to accept the terms so check the first box.
6. Then, copy the Panda 3D 1.9.0 into your C: drive. Don't move it! Copy it. It may take a while, but it'll be fine.
7. Okay, ready to play? Good! Go to src-feature-the-experiment ---> astron ---> win32 and then run start.all.bat
You'll get 3 cmd windows, but don't worry. They're safe.
8. On the AI server, press enter twice and on the Uberdog server, press enter once. You'll have to wait until it loads all the playgrounds and stuff.
9. Once it generates the game and connects to the game, you can go back to src-feature-the-experiment ---> win32 ---> start.game.localhost
10. Type in a unique username. It's like your password, so you don't want anyone to know it.
11. There you go! You should be in Toontown Infinite.
***The Experiment instructions***
1. Wanna play the unreleased feature from Toontown Infinite? Okay! Go to the red ropes or whatever it is and type in ~collisionsOff. Once you're in, type in ~collisionsOn.
2. Say 'Hi!' to the red monkey, and then you should be in the Experiment. Type in ~collisionsOff to get out and ~collisionsOn to not make you go through things.
And there you have it! A long, but helpful tutorial on how to setup the Toontown Infinite source code.