I clicked on the download button and downloaded 429Mb, doubled clicked on that and got a wizard. a box appeared which gave the option of installing the plug-in to a particular program. I suppose I should have realised something was wrong at this point, because if things had been working properly it would have automatically installed it to PS. I myself specified PS.
I don't recall seeing a specific message during the running of the wizard warning of 64 bit/ 32 bit incompatibility, and the wizard closed and seemed to imply that installation was successful.
I have to say that it was my own stupidity in not reading the fine print properly which was the cause of my woes. Hopefully Dave's offer of the original version will get me up and running again.
I have not mentioned here before (for the sake of brevity) that I did try finding the specific files for SEP2 amongst those downloaded, and manually moved them into the PS plug-ins folder. I then deleted all of the other downloaded files, eg Viveza etc. I actually got the normal PSE2 to display on the screen. It seemed slow, and then I lost it after closing it. But presumably there is simply no way it would work on my machine in its present state?