A day behind schedule, Beta 3 is out. (CAUTION: DIRECT LINK TO 370MB ISO) It was actually finished a few days ago, but the hoster had more important things that needed to be done (understandably), and so it didn't hit mirrors until today.
Another important update: SLAX 6 RC3 IS OUT, and it uses Glibc 2.5! If you recall, the only reason I didn't use SLAX in the first place is that it used Glibc 2.3, which SuperTux simply can not run on. Since SLAX can make a tiny CD image, it will most likely be the final base system.
Related note: So far, everything one needs to run SuperTux is integrated onto one .lzm (SLAX 6 or later) module. This means SuperTux Milestone 1.9, OpenAL, PhysFS (with soft links so that it'll work), and two bonus levels. I might put it up for separate download if you happen to have SLAX or Wolvix already, but just having a CD is still a good idea.