Wha? Pretty sure that there is a WinRAR MAC version, just download the program, right-click the folder or the files you want to send and add it to archive, if the file is excessively large, like close to or above 1gb, then just divide them up and archive/upload them seperately, RARing and uploading each set of files.

I don't have a Mac, but I can't imagine it being all that different.