The arduino used in that solution is not running at 12V. Only the ATtiny RST is jolted at 12v. The resistors are there, I presume, to protect the arduino from high voltage signals.
Note that serial high-voltage programming is not appropriate for all ATtiny processors. For some, you use parallel
high-voltage programming instead.http://support.atmel.no/knowledgebase/a ... mming.html
The Atmel STK500 supports high-voltage serial programming through avrdude. Special timing is required for this process (see page 159 of the ATtiny45 datasheet
for an example). If you hooked up the usbTiny correctly,I don't know whether or not it's avrdude profile would support the proper sequences.
I think your best bet would be to use an arduino, as in the solution you linked to, or simply get an Atmel STK500.