• Locate core_build_options.h in the Tiny Core directory
• Open it in your favourite text editor (I like Visual Studio)
• Navigate to line 107...
http://code.google.com/p/arduino-tiny/source/browse/trunk/hardware/tiny/cores/tiny/core_build_options.h#107
• Change TIMER_TO_USE_FOR_MILLIS to zero...
#define TIMER_TO_USE_FOR_MILLIS 0
• Save and close the file
• Re-upload your program (generally it is not necessary to restart the Arduino IDE after this kind of change)