and will the 7-zip or whatever work with winzip?
Yes, it will work with .zip, .rar, .7z, ... .iso, .lzh, .001, .arj, .bz2, .cab, .cpio, .deb, .gz, .rpm, .tar, .z ...
Supported formats
Currently 7-Zip supports the following archive formats:
7z
ZIP
GZIP
TAR
BZIP2
RAR (only browsing and decompression)
CAB (only browsing and decompression)
ARJ (only browsing and decompression)
Z (only browsing and decompression)
CPIO (only browsing and decompression)
RPM (only browsing and decompression)
DEB (only browsing and decompression)
LZH (only browsing and decompression)
SPLIT (only browsing and decompression)
CHM (only browsing and decompression)
EDIT: And no, 7-zip does not take over your file associations unless you tell it to via Tools>Options. But, you can right-click on any file, go down to "7-zip" and open it. If you mean does WinZip open .7z files, it does not appear so from WinZip's site. I know the latest version of WinRAR does.
BTW, if your dad has problems with 7-zip, tell him that it is an open source software from
SourceForge.net. If he doesn't like it, he could join the 7-zip programming team, and help out.