Right before the installation completes, I get this error: "expression error runtime error (at 16:21) Invalid floating point operation", then I get: "Invalid Opcode", after which installation finnishes like nothing happened. If I try to launch the game, I get this message: d3dx9_30-dll missing" and the game won't start.

According to different topic (It won't let me post links here, who come up with this retarded idea?) it's a problem GOG has with latest AMD drivers. Of course, I'm not sure it's the same exact problem, but it seems like it... Anybody know how to fix this? I mean are people from GOG at least looking at it?

The "d3dx9_30-dll missing" message indicates that you are missing DirectX 9, so you will need to install that. You will still need DirectX 9 even if you have the latest versions; it will install alongside your other versions without overwriting them.

Also you may need to update your video card drivers.

I'm pretty sure I have DirectX9 installed cause I play other games, but I still tried install it again. Alas, no help. Same error during installation, same "d3dx9_30-dll missing" message when trying to launch the game. I also have the latest amd drivers, which, according to different member of this forum, are colliding with GOG installers. But as I said, I'm not sure if that's what's happening here...

Ok, so I tried install like 5 different DirectX9 variations from microsoft page and after installing them all, the game finally worked! I guess I was missing some particular version, which wasn't packaged with my already installed games (they're all new/really old). Although I still get the errors when installing (runtime error, invalid floating point operation, invalid opcode), but the game launches. I'm afraid there might be some problems later because of the errors during installation, but so far, everything seems to be alright.

Thank you

Glad you got it to run! If you have problems later on, just post here and I or someone else can try and help you sort things out.