The detailed iTunes requirements for Windows hardware and software are included on this page:
http://www.apple.com/itunes/download/
The basic hardware requirements stated are:
"+A PC with a 1GHz Intel or AMD processor+
+Screen resolution of 1024x768 or greater+
+Playing videos purchased on the iTunes Store requires an Intel Pentium D or faster processor+"
It would seem that your machine doesn't meet the screen resolution, and possibly not the processor requirements.
Message was edited by: modular747