I have uploaded USBasp drivers for windows 7 on megaupload. Drivers can be downloaded from the following link:
1) Download and extract contents into some folder.
2) Connect USBasp to PC. Go to Device Manager, locate “USPasp”. Right click and select “Update Driver” .
3) Browse for extracted folder and proceed as usual.
4) “Windows Security” warning will appear. Select “Install this driver software anyway” and proceed.