5. I've never heard of ACR updates being compressed in a WinRAR format - Adobe always uses ZIP. However, a great tool for decompressing any archive format (and compressing in seven types) is 7Zip - free download here. It's a very handy little program.
There are numerous programs for opening Zip files, WinRar is one of these and is obviously the program the OP uses for opening Zip files. It also happens to be the one I use and opens all Adobe Zip files.