I can run OP on Windows 7 with no modifications other than latest Taldren patch and OP+. Others can as well. Single-player, GSA, and IP modes work fine in Windows Vista and 7, at least in every machine I've ever tried it on since Vista was released.
The only thing that does not work (with OP and EAW) is the Dynaverse, at that is due to an incompatibility. It is a known issue. As stated, a fix is on the works for EAW.
What exatly happens when you run OP? Perhaps I can help. I also see you got EAW working, so perhaps its not nessecery. Either way, I will do what I can to help.
Strat