I just discovered a really simple way to install USBasp driver for all versions of Windows. This is by using a driver installation tool called Zadig. It provides signed drivers for libusb, which means a lot of open-source USB drivers (including USBasp and USBtiny) will now work perfectly on Windows 7, 8, 8.1, 32-bit, 64-bit, without messing with driver signature enforcement! Check my blog post from last night for details:
http://rayshobby.net/?p=9912
This apples to all OpenSprinkler 2.0, 2.1, and SquareWear users. I will be updating the user manual and instructions right away.