I have no problem with SR4 myself, but you can try this. First, make a copy of the Poser5 folder including subdirs (if you have disk space, obviously), and call it "Poser 5 copy" or whatever. Then, try to install SR4 on this folder changing the path in the installer, and open Poser via the exe file here and not from the start menu; as the only entries I found in the registry that are Poser related are the PZ3 default application and some links to help and readmes, I think it should work normally and you have the original version still intact (apart from the paths in the registry and the links in the start menu, now supposedly pointing to the "copy" folder). Optionally, if you don't want to screw up the registry or the start menu, you can even install SR4 on the original folder; then, if something goes wrong, you simply re-copy the backup folder over this original one and everything would return to the previous version. Hope this help.