What a nightmare! Today I tried installing the Sony rereader software on my Windows 7 Pro (64bit) machine, so I could load some books from Books on Board. Download Adobe Digital Editions, and registering that side of things went well! Installing the Sony software seemed to work, but I couldn't get it to actually open up! At all....
After fiddling around on two seperate machines, both running 64bit Windows 7, I decided to give up.
XP Mode to the rescue!
Turns out the Sony Reader software, as well as Adobe Digital Editions play nicely together in the virtual XP mode provided in Ultimate and Professional! Just install everything as normal, and click the USB menu and then the Sony item and everything works as you'd expect! Woo! Now I can enjoy some Terry Pratchett without resorting to actually buying a bit of a tree!

