Typically, getting a 500 error after uploading a .htaccess file is due to permissions. Did you setup this server yourself from scratch? Also, are you uploading files as "root" or as a normal user? The issue here would be that you need to make sure that your .htaccess is uploaded by a user that the Apache web server user can read the files of. If this is not the case, you will need to change the ownership of the .htaccess file to the user that Apache is running as.