I installed the latest WDK 7.1 and entered the windows xp free build enviroment.
E:\Drivers\openvpn-2.2.2\tap-win32>build -cef
BUILD: Compile and Link for x86
BUILD: Loading e:\winddk\7600.16385.1\build.dat...
BUILD: Computing Include file dependencies:
BUILD: Start time: Mon Apr 09 20:03:02 2012
BUILD: Saving e:\winddk\7600.16385.1\build.dat...
BUILD: Finish time: Mon Apr 09 20:03:03 2012
BUILD: Done
No sys file is found under i386 directory. Please help me out, thanks.