You know I'm ashamed to say this, but I completely messed up the original install. OM and OMEGU come in packaged folders, which I completely failed to unpack into the mods folder.
I did the RTFM thing and this became painfully obvious, so now I have the game properly installed. It has crashed a couple of times but so far the last saved position has loaded fine and I'm saving pretty frequently now. I've got multiple installs and I've started keeping each versions saved games in its own folder, which I rename before changing games. So far doing it this way has given me zero hassle. If I make it as far as a conning tower upgrade, I'll let you know how it goes
