When you download a file to the desktop and it is a zip file icon, you doulbe click on the zip file. The zip will be uncopressed by the mac and 1 or more package. files, usually a read me file and sometimes a JPEG file will appear on the desktop.You can read the read me file and then bin it and you can look at the JPEG file  but the only files that you put into your downloads folder is the package. file. The folder is found in Users/ your name/documents/EA games/TheSims2/Downloads
rar. files may need 'Unrar' for mac which is a free download and should be easily found via google . You do the same double click on the rar icons and place the decopressed package. file in the downloads folder. If you are downloading a whole sim or building, or sometimes walls and floors they may come as a Pack file . These files DO NOT go into the downloads folder. you double click on these icons and the Pack installer dialogue box will appear, just follow the instructions. Don't try to install Pack files while you have the game running, wait until you have quit the game.
On some sites you may find some cc that you want, and it says that it is a rar. file, but when you try to dowload it all that happens is you get a whole load of text in the browser window and nothing on the desktop. This is because there are differant types of rar. files out there and creators don't all use the same programs to make their content. The Mac will sometimes find these files difficult to see and will not download them. The way around this is to control/click on the download link . a pop up will appear, click on  'download file to desktop'. A txt. file will appear on the desktop and you just drop it onto Unrar and it will be decompressed onto the desktop as package. file , etc.
Hope this helps anyone finding all this a problem

This is a really horrible arguement going on here. The cc that you all make is so fabulous and makes playing the game possible.I think my interest would have been over a long, long time ago if not for the work of everyone who makes beautiful objects and sims to replace the hideously ugly maxis content I don't think that it is unreasonable for people to want a little recognition for their work, and to some extent it is also reasonable to maybe get a little monetary reward. Is there no possibility that creators who need to be paid could come to some agreement with EA where EA actually buys their work from them and then offers it for sale as EA product listing the artist as creator?
It seems to me that this would be an arrangement that would suit all. Creators who want to do this as a career could get paid for their work, EA would, at last, have truly creative people working for the game, who were artists and not just computer nerds, and those who just like to make things for other simmers could still offer their work for free.
EA must know by now that their games just would not sell as well as they do if it were not for all the fabulous stuff available out there that really has very little to do with them. I think that if you all used your time and energy in this direction instead of arguing about the intricacies of patent law, etc. something positive and enriching for the whole simming community could result.