This worked great for me too, on Win7 Home Premium 64-bit.
Download the ZIP file from Jeff's page, then unzip it and keep track of where it puts the unpacked USBtiny.inf file. Then go to the Device Manager, locate the not-working USBtinyISP and upgrade the driver - manually locate the .inf file. It'll complain about the driver not being signed, but it will install it if you persist, and then no more complaints!
(With the reservation that I haven't actually tried programming anything with it just yet - but at least the driver installed. )