Canon’s site for the LiDE 50 does not list any Windows 7 drivers for download, nor Vista 64-bit drivers. However, I did find that you can use the CanoScan LiDE 60 drivers in place of the LiDE 50 drivers, and they do have options listed for Windows 7/Vista in both 64-bit and 32-bit varieties.
Do do this, you download the appropriate driver (either the Windows 7 64 or 32 drivers) which is contained in an executable file. Use a program such as 7zip to uncompress this file into another folder. Within this folder, there are no drivers but further cabinet files. Use 7zip to decompress the _winzip_ file, which actually contains the driver you need to install.
In your device manager, locate the scanner and select the option to update the driver. You will need to select the driver manually, then specify the device type and driver, then click the “Have Disk” option. Locate the folder where the driver is located and select the .inf, and it will successfully (hopefully) install the LiDE50 as a LiDE60 scanner.
After having the device installed properly, download the latest CanoScan Toolbox, of the date of this writing it is version 188.8.131.52. This will give you access to all of the options you should have to set the buttons on your scanner, for example.
No need to buy a new scanner just because Canon didn’t develop a driver for the LiDE 50, apparently the chipset for the 60 is almost exactly the same.