In the scenario you described with a 64G SSD boot drive and another 500G HDD for data, if you dragged a file onto the desktop, it would be saved on the SSD because that's where the OS and desktop are. Putting files on your desktop is not the best idea anyway so it would be better to create a folder like "My Data" or whatever you wanted to call it on the 500G HDD. It would probably appear with the drive letter D: or E: depending on what other drives you have in your system. If you are using Win 7, you could set things up so that the contents of the "My Data" folder on the 500G HDD would appear under the "Documents" Library in Windows Explorer or "Computer".