I have a rebel xt and recently a pc with windows 7 (64-bit). (I didnt have any problems with my XP PC, but alas, it had to be replaced.) I have switched from PC connection to PTP. Windows popped up an info box stating that drivers were being installed, then it said the driver could not be installed. My rebel shows in my computer as a canon eos digital rebel xt, yet, while connected to the PC, my camera flashes "busy", and continues to flash "busy" for as long as its connected. (the camera works great, otherwise.) When I switch back to PC connection, the camera is not recognized, but it does not flash "busy" when powered on. I have the latest firmware and zoombrowser ex installed. Any ideas?
Canon's programs have had compatibility issues with Windows x64 (although they've been working OK on my Vista 64).
Perhaps check that you have all the Canon programs installed and updated. Also, I'd invest in an external card reader in stead of hooking up the camera directly via USB. Card readers are cheap these days and I've had two of them work fine with my Zoombrowser on Vista 64 so far.