Here's how I do it (Win7 Pro 64bit):
Create folder
OpenXcom, create two folders inside:
data and
user (I like to keep the settings/saves inside the game folder).
Inside the Steam installation folder there is a folder called
XCOM. From this location you copy the following folders:
GEODATA,
GEOGRAPH,
MAPS,
ROUTES,
SOUND,
TERRAIN,
UFOGRAPH,
UFOINTRO,
UNITS. These are all the folders/files you need.
So the file structure right now is something like this:
OpenXcom /
=> / data /
=> / GEODATA /
=> / GEOGRAPH /
=> / MAPS /
=> / ROUTES /
=> / SOUND /
=> / TERRAIN /
=> / UFOGRAPH /
=> / UFOINTRO /
=> / UNITS /
=> / user /
After this download the universal patch and extract its contents
inside the
data folder,
overwriting the existing files.
As a side note (this is just how I do it, so it's optional) I delete all the files inside the folder
SOUND and go to
this site and download the preffered
Music and
Sound files. As an example, I personally use
Playstation (PSX) music set in OGG format and
Original UFO: Enemy Unknown 1.0/1.2 DOS Sound Effect Set, others might have different preferences.
At this point I would archive the whole
OpenXcom folder, give it a name like
OpenXcom-data and keep it somewhere safe, such that I have a "clean" data set and to not have to repeat this whole process again.
Next step is downloading the prefered nightly, put it in the same place as the OpenXcom folder an extracting it in place. There should be no problems (at least I haven't had any).
Good luck