For Windows:
To get around this issue, please go to the game's folder: (...)The Witcher\System\witcher.exe and create a shortcut to witcher.exe.
Right-click the shortcut and go to its Properties. In the Target textbox next to the path type:
-dontForceMinReqs
There should be a space between the path and the switch, like here:
"(...)System\witcher.exe" -dontForceMinReqs
Confirm with OK. Now when you run the game from this shortcut the Witcher should stop announcing that the minimum requirements are not met.

For Mac OS X:
Please go into your Applications directory. Right-click The Witcher.app, and select "Show package contents". Go into the Contents directory and open the Info.plist file.
Find this line:
Program Flags
Underneath it, you will find this line:

Change the second line to:
-dontForceMinReqs
Save the file and try launching the game now.