Hi, I'm the maker of the Nostalgia track.
To start, try checking out the links in the
Artwork Section of the Get Involved page. Particularly useful is the
Track Maker's Guide, which contains links that go over all the steps setting up and making a track, as well as documentation for the track making tool.
One of these links tells you how to install all the tools you'll need to edit a track. The newest version of the tools seems to be incompatible with the current stable release of supertuxkart, so make sure you download the zip containing all required files, instead of getting the files from the media repository.
Once you have everything installed, you have to find a way to get the old versions of the tracks. Some of them are in old revisions of the
media repository (change the number in the url to change the revision you're viewing (around 4000 seems to have the most of the old tracks)), but a lot aren't. For these tracks, I downloaded an
old version of the game itself and imported the various files required to piece together the tracks models. The models are stored as .ac files though, so you'll have to find a way to open these with Blender. I have an addon of unknown origin that will do this.
When you've got the track models into Blender, you'll have to fix the textures. All the textures in the old version of Supertuxkart were stored as .rgb images and should be converted before they're used. The mogrify command in
ImageMagick should be able to convert an entire folder of files at once (mogrify --format png *.rgb). Also, a lot of the textures in the Blend files reference locations from the original developers' computer, which you won't have. Replacing each image with its corresponding converted png will fix this.
The last main step is to add nitro and items. The locations of these are stored in .loc files, found in the data directory of the Supertuxkart game. I have a script that will automate part of the process of reading the locations and adding items.
Of course, there's also a lot of smaller things that you should be aware of. For example, some tracks have a unique sun/ambient light colour, and some materials will slow down the kart when driven on.
If you have any questions about any part of the process, feel free to ask me.