The .rar file the author is offering is an archive file just like a .zip file. Depending on what you're using to unpack archive files, you should be able to use a .rar as you use a .zip. Since I use a program called 7zip (7-zip.org), all I have to do is right click the .rar file and tell 7z to extract it to a folder (again, just like one would unpack a .zip). After that, I open the folder 7zip extracted and run mugen.exe
I'm not sure why you specifically want a zip file versus any other archive filetype. Perhaps if you explained why, someone would have helped you by now.
It's pretty uncalled for and shitty of you to talk like that to someone who is offering things for free. With minimal internet research, you could have found the answer. I understand you're frustrated, but check yourself next time, please. The author owes you nothing.