downloading

I have downloaded the mac "locomotive" many times and receive a "codec
overrun" error. I am at a loss. I have read that this means a
damaged .dmg, Any help is appreciated.

  Machine Name: iBook G4
  Machine Model: PowerBook6,5
  CPU Type: PowerPC G4 (1.1)
  Number Of CPUs: 1
  CPU Speed: 1.2 GHz
  L2 Cache (per CPU): 512 KB
  Memory: 768 MB
  Bus Speed: 133 MHz
  Boot ROM Version: 4.8.7f1