You may also need this x3 It opens the files when you download them so specific files such as .mp3 and sky files can be placed in the correct folders. http://www.win-rar.com/download.html?&L=0 (http://www.win-rar.com/download.html?&L=0)
Oh darlin, you don't really have to buy it haha. Download the 40 day trial and you can use it forever. Once the trial is over, everytime you open something with WinRAR a small box will pop up, just click the 'x' to close it. I've been using winRAR for years. Once you have WinRAR, after you download the map and see the white box at the bottom, just click it and winRAR will automatically open it. If not, then when the other window pops up hit "Choose from installed programs" and find WinRAR.
So welcome! If you have any more questions or need more help please let us know, we'd be glad to give ya a hand ^-^