Steam version of Fallout / Fallout 2 in a window

Unfortunately, I don't believe Steam for OS X will let you even download a Windows app you buy through Steam. I suppose you could drag and drop the game files, and then restore the game from the copied files, but I'm not sure whether that works between platforms.

And because Steam usually tries to launch all Steam games itself (at least on Windows), I don't think it would be possible to force a game to run under Wine unless Steam itself consents. You may be able to run non-DRMed games directly by double-clicking the executable, but I am unsure about this.

Adding Minecraft (Java 64bit) to Steam

1. Open the command line prompt as an Administrator. Usually, you can find the command prompt in the Accessoires start menu; right-click on it and chose "Run as administrator", accepting any UAC prompt which pops up.

2. On the command line prompt, make a local symbolic link to the javaw.exe executable by typing in the following:

   mklink %AppData%\minecraftjava.exe %ProgramFiles%\Java\jre7\bin\javaw.exe

   Replace jre7 with jre6 if you still have Java 6 installed instead; replace the whole Java path if you installed it into a different location.

3. Try out the new executable with the following command:

   %AppData%\minecraftjava.exe -jar %AppData%\.minecraft\minecraft.exe

4. Open Steam and in the bottom left, click "Add a Game", then "Add a Non-Steam Game"

5. Click on "Browse" at the bottom
6. Navigate to wherever "%AppData%" is on your computer (it's usually in C:\Users\Username\AppData\Roaming) and choose "minecraftjava.exe"
   
   You can verify the location of the %AppData% folder by opening up a Windows Explorer (Windows+E or right-click on the Start button and chose "Explore") and typing it in the location bar at the top of the window.
7. Click "Add Selected Programs"
8. Right click on the entry made in your Steam Library and click "Properties"

9. Set the target as this (on one line, including quotes)

   "C:\Users\Username\AppData\Roaming\minecraftjava.exe" -jar "C:\Users\Username\AppData\Roaming\.minecraft\minecraft.exe"

   Again replace "Username" with your Windows user name.

10. Click "Close" to save that change.

To set the icon:

10. Right click it again and click "Properties"
11. Click "Choose Icon"
12. Find your Minecraft.exe file ("C:\Users\Username\AppData\Roaming\.minecraft\Minecraft.exe")
13. Click "Close"
14. You may have to set the target to what it was set to above again. (After clicking "Close") because for some reason Steam will forget parameters after changing another setting.

Minecraft should now be able to run via Steam, with support for showing your "In Non-Steam Game" status and with the Steam Overlay.

If for whatever reason it does not work, go back into properties and change to target to what it was set to above. When using parameters Steam sometimes forgets this under other circumstances.