Before you installed it, you need to change the compatibility. Right click and choose Properties and set compatibility mode to Vista Service Pack 2 and run as administrator. Now you can install the Ext2Fsd-driver.
Ext2Fsd only supports ext2 and ext3 formatted volumes. To make Ext2Fsd can read ext4-volumes, we should patch it. Download the patch from http://www.acc.umu.se/~bosse/ (Ext2fsd-0.48-bb8)
Unzip the downloaded file. Open the folder fre and choose your architecture. (i386, ia64 or amd64)
Copy ext2fsd.sys to Windows\System32\drivers. (Keep the original file as back-up)
If you haven’t the amd64-architecture, you can restart your computer.
Now you can mount your ext4-drive, by opening Ext2Mgr and select your ext4-volume, which you want to mount. Choose a mount point!
If you have the amd64-architecture, like me, then you have to sign the patched driver. If you reboot and choose (just before Windows is loading) F11 and choose advanced boot options (F8) and select Disable enforced driver signing, then Windows can use the new driver. You have to do this each time you boot Windows 7. Fortunately, there is an easy way to load an unsigned driver in Windows 7 (or Vista 64-bit).