Unfortunately, Sony does not support this recorder under Win7 64-bit. See http://esupport.sony.com/US/perl/swu-list.pl?mdl=ICDP520&SelectOS=27
for the available drivers. You can try the Vista or WinXP driver with the compatibility mode. (This may involve allowing unsigned drivers since there is no information on 64-bit compatibility on either the Sony or Microsoft Vista Compatibility site.)
To try this, download the driver and right click on the installer. Then choose Properties and then the Compatibility tab. Turn on Run program as Compatible with the appropriate OS. Then right click again on the installer and choose Run as Administrator.
I do not know if this will work. A method that will work is to use a computer (virtual, dual-boot, or true second machine) with an older version of Windows installed. If you have Win7 Pro or Ultimate, you can create a virtual XP computer for free. Download and install Virtual PC and XP mode from Microsoft. Install them in order. Then install the XP software from the above site in the virtual computer and it will work. (Other virtual computer programs are Parallels and VMWare.) All of the other options will require a licensed version of the older Windows OS. Please note that the virtual computer can't share files directly with the main computer. You'll need to save files to external or removable media (optical media or flash drive, for example) to share them.
I hope this helps.