System Requirements 

Windows Minimum specs:
  Windows 98/ME/2000/XP/Vista
  1.2 GHz Pentium 4 (or other equivalent)
  128MB RAM
  GeForce 2 (or other equivalent)
  150MB of hard drive space

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)
  128MB RAM
  GeForce 2 (or other equivalent)
  150MB of hard drive space

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

Linux Minimum specs:
  Not sure yet on minimum Linux distribution
  1.5 GHz processor (x86 or x86-64)
  256MB RAM
  GeForce 2 (or other equivalent)
  150MB of hard drive space

Linux Recommended specs:
  2.0 Core Duo processor (or better) (x86 or x86-64)
  512MB RAM
  GeForce 3 or better (or other equivalent) 

Mac OS X 10.3.9 should also run Depths of Peril fine, but you need OpenAL installed first.  You can download the OpenAL installer from Creative.

As always system specs are very subjective.  If you are concerned about whether or not your computer can run the game as well as you would like, please download the Depths of Peril demo and find out.