Just thought I'd add in my 2 cents. PSPX4 wouldn't run on initial installation on Win8, even if I tried compatibility mode. Complained about the program not being compatible, or something similar. Saw the post here about installing SP1, tried that and then the program wouldn't even launch at all, no response whatsoever. Then I tried installing SP2, and what do you know, its now working without any issues.
Also, FWIW, I was able to install PSPX2 and get it to run on Win8 the first try.