Yeah, well, from what I hear fan sites are illegal. As is fan art and any kind of fan fiction. Basically this whole site could be considered illegal. I don't see any reason to single out this project. But even if fan sites are illegal that doesn't stop sites like this from appearing. Besides, many publishers enjoy the free advertising they usually amount to, or at least enjoy that fact that someone has enjoyed their work enough to make their own derivatives of it.
Besides, who would you ask for permission? The company that originally produced it doesn't exist, so you can't ask them. The company that bought out that company doesn't seem to acknowledge the existence of the game, so what are they going to say? And even then, who exactly do you ask? Most people here don't really know what the exact status of the copyright is, or who owns it, and even if we did, who in some big corporation would we ask who actually knew something about it or could give permission.
I'd say if you enjoy doing it, then go ahead and finish it. If someone actually took offense to anything on here and had some legal claim to the copyright, then I'd imagine they'd just ask us to take it down and we'd do it. Besides, gpgarrettboast is right. If they wanted to cause trouble over copyright issues, it would have been done long ago. And keep in mind that people who worked on the design of OP2 know about this place and have either sent or replied to emails here (positively).