Hi! Thanks!
Yes, I think the problem was I foolishly chained old keyboard interrupt handler to mine (first experience with it). I fixed and reuploaded it, sorry!
Great! If it's desktop Celeron 266 then it's Covington without L2 cache and quite a bit slower than Pentium II or Celeron Mendocino. Memory subsystem speed is quite important for this type of engine, there is ~330 thousands memory lookups per screen for terrain height and color. Probably even Pentium 233 MMX with L2 cache on motherboard can be faster I think (but right now I don't have the hardware to try, so than you for testing!