508.zip contains the newest drivers for Windows, including Windows XP (32-bit only) support.

"sddr55v506.exe" is a self-extracting archive which will only run on older (not x64) systems, but contains the same content as the "sddr55v506" folder.

There doesn't seem to be any reason to prefer 5.06, but it is included anyway.

The 5.06 install packages are also included within the "sandiskv506.iso" which originally shipped with the hardware.