How to use precompiled binaries
1) Download the screensaver package.
2) Extract it somewhere.
3) Put the original TTD data files (sample.cat, trg1r.grf, trgcr.grf, trghr.grf, trgir.grf and trgtr.grf) into "data" directory.
4) OPTIONAL: Copy your favorite OTTD savegame file into the "save" directory and rename it to screensaver.sav. Make sure the savegame is compatible with trunk revision 14030 (stables 0.6.2 and older are compatible). Make sure there are at least several signs defining individual camera views or the camera would be static.
5) Download the OpenTTDCoop GRF pack 7.1 and extract it into the data folder if you want to use the included demo game. Make sure there are all the GRFs your savegame uses if you are not using the demo game.
6) Enter the directory and right-click on the openttd.scr. Now choose "Install".
7) Windows screensaver dialog will pop up. Make sure correct timeout is selected.
8 ) OPTIONAL: Click Configuration. Seemingly unmodded OpenTTD will open. Now make sure valid screen resolution is set and fullscreen mode is ON. The screensaver looks very weird in windowed mode (but starts and quits faster). You can also adjust some more settings. You can later access the configuration mode by right-clicking the openttd.scr (the screensaver file) and schoosing "Configure" or by right-clicking desktop, choosing "Properties", then going to "Screensaver" tab and clicking the "Configure" button.
It is done, now you can test it

How to compile it yourself
1) Apply the patch on r14030 source as described in this thread. Or use BuildOTTD and then skip the step 4.
2) OPTIONAL: Apply any third party patches - screensaver should be compatible with most of them
3) Compile the patch using any compiler you like.
4) Rename the resulting openttd.exe to openttd.scr.
5) Continue with step 4 of "How to use precompiled binaries"

Known issues
- takes some time to load and quit (this is much faster in windowed mode, but it looks weird)
- no support for non-windows platforms and Win98 and older. Please confirm if it works on Vista and 2000.
- no support for passwords (at least it seems)
Version history
Version 1
- first public version
Version 2
- the camera now jumps randomly over the signs
- demo game present (requires OpenTTDCoop GRF pack 7.1)
- fixed many negative effects caused by the time flow (crashes, industry closures, new vehicle screens, town growth...)
- mouse movement now shuts the screensaver down (= the application now behaves fully as screensaver)
- updated to r14030