My understanding is that Half-Life will run correctly on W2K. The file system has nothing to do with the game running, as the game has no idea what file system is being used. The only caveat is to make sure you have the permissions set correctly. You will probably want read/write access to that directory, so you can either assign the rights to a User account, or use an account that has been given Power User rights which should have those rights automatically for the directory if Half-Life is located in Program Files.