To zip file(s) :
ShellExecute(0, 'open', 'Winzip32.exe','-a a:MyZip.zip *.dbf *.mdx *.dbt' , nil, SW_NORMAL);
To unzip file(s) :
ShellExecute(0, 'open', 'Winzip32.exe','-e a:MyZip.zip', nil, SW_NORMAL);
More information on http://www.winzip.com/wzcline.htm