after reinstalling Windows, Steam and Eufloria on your computer, you could use "Unlock" in the main menu to unlock the story mode and skirmish areas.
However, i think that way you cant unlock all Dark Matter levels.
To keep your status exactly as it is, back up the file "user.settings" from C:\Program Files\Steam\steamapps\common\eufloria\Resources\ and restore it to that location after re-installing; that file contains your settings and your level progress. If you have custom maps and want to keep them, you will have to back them up from the "maps" folder within the Resources directory, and restore them respectively.
PS: you might want to try that out first, e.g. by renaming user.settings and see how the game behaves, then restore it back and see if the progress is restored. Otherwise, I made you lose all your progress D: (In that case, i will do evrything i can to get it back for you)