I have both, when i try and open .rar or .01 .02 etc files sometimes z-zip complains about the file being broken

N00b.
If you have .01, .02, .nn, you unrar the .rar. If you have xxx.rar, you unrar the first one.
I use 7-zip exclusively and I've never had it fail on an uncorrupted archive.

There are other free utilities that deal with .RARs, ie. ALZip etc, see "Compression/Decompression" section in link in my sig for more of them.
ALZip will become Payfor in the future that's why i have switched to IZarc.