Windows Minimum specs:
  Windows 98/ME/2000/XP/Vista
  1.5 GHz Pentium 4 (or other equivalent)
  256MB RAM
  GeForce 2 (or other equivalent)
  200MB of hard drive space
  DSL or better for multiplayer on internet

Windows Recommended specs:
  2.0 GHz Pentium 4 (or other equivalent)
  256MB RAM
  GeForce 3 or better (or other equivalent)

Mac Minimum specs:
  OS X 10.4 or 10.5
  1.5 GHz processor (PowerPC or Intel)
  256MB RAM
  GeForce 2 (or other equivalent)
  200MB of hard drive space
  DSL or better for multiplayer on internet

Mac Recommended specs:
  2.0 GHz processor (PowerPC or Intel)
  256MB RAM
  GeForce 3 or better (or other equivalent)

Mac OS X 10.3.9 should also run Din's Curse fine, but you need OpenAL installed first.  You can download the OpenAL installer from Creative

Din's Curse also seems to run fine in Linux using Wine.