5.5 pro does have 3d capability. That plugin is 64 bit make sure your system is 64 bit before installing.
The folder location of photoshop 5 (64bit) is
C:\Program Files\Adobe\Adobe Photoshop CS5 (64 Bit)
Check your folders if you have 5 and 5.5 you could have two folders each having its full name as part of the folder name.