Check the Arduino support pages on the Arduino web site, there is a way to use one Arduino board as an USB ISP programmer for another.
The USB tiny *might* actually work to program devices >64K. There is a patch to AVRdude that disables the auto-verify function which seems to be what fails due to the firmware in the USBtiny. The device may actually program but the USBtiny can't perform the verify beyond 64K.
Needless to say there is some risk in using the device without the verify function! Otherwise just buy an AVRispMKII or a clone of one. The real deal will cost you about $35 US from Atmel. I now have both the USBtiny and the AVRispMKII myself having started using atmega1284p chips.
See the bottom of this page: http://blog.lincomatic.com/?p=548