I imagine at some point there will be a stickied "how to" for Win 7 & 8, but here are my experiences today:
specs: custom built Intel i7 3.5GHz, 16GB RAM, Win8.1, Nvidia GeForce GTX 570
-Antivirus/windows firewall off, running installs as Admin, compatibility for setup.exe set to Win XP service pack 2
-I was trying to load OP from the ISO I purchased last yr, using VirtualCloneDrive to mount but wouldn't get past the menu screen from autostart. Same ISO & program worked on other machines, so I switched to trying to load from the older actual CD, same problem. After trying several iterations of compatibility settings I noticed that the setup.exe was listed several times in task manager from every attempt I made, and that the process tree was getting stuck by "Adobe CEF helper.exe", which was running from my Adobe Creative Cloud account. Stopped Creative Cloud, and install proceeded normally
Long story short, think about what your machine might be running in the background and turn off before installing OP. I had stopped email clients, antivirus, etc., but only foound my problem after staring at Task Manager for a few minutes
Install went into the "Program Files (x86)" folder. As I thought I remembered reading here that it should go into "Program Files," I moved it. OP ran thru startup, crashed 30 seconds into a game. Tried running the 2500-2552 patch, it would start but it would fail out. Noticed then that even if moved, it defaulted to trying to find & patch the game in the "Program Files (x86)" folder. Moved the game back to "...(x86)" and patch worked.
OP now launches, with 2.5.5.2, but still I crash after a minute or so of play.
Also, I get a "this won't run on your PC" msg whenever I try to run the OP_DLL_Updater, even when it is in XP compatibility/admin mode. Wondering if I can grab the appropriate DLLs from another machine I have it installed on.
Feels like I'm getting closer; at least it's installed, and now it's a stability problem