Jaf (J.A.F) is the best tool to flash Nokia mobile phones. The tool is used to flash and unlock many Nokia mobile phones including both new and old models. If you are using this flashing software already to flash and unlock your Nokia mobile phones, then there is a good news that J.A.F 1.98.66 beta is available for free download. The previous versions were reported as creating bugs in Windows 7 and Windows 8 but the recent release is bug fixed and more stable and you can install this software in Windows 7 or Windows OS and can flash your mobile phone comfortably.
Although this install should work perfectly in Windows 7 and Windows 8, still if you are getting errors, you can try the crack at Symbian Forums here. Someone has shared the crack there which will help you fix the bugs which are created in Windows 7. But I hope that you will not need the crack as this download of J.A.F 1.98.66 is bug fixed and stable and will let you flash your phone in any OS including the latest Windows 8. You can download J.A.F 1.98.66 here.