You can use the following code:
declare @Command as varchar(5000)
set @Command = 'C:\Progra~1\winzip\wzzip.exe "H:\SQLBKUP\test.zip" "H:\SQLBKUP\test.txt"'
exec master.dbo.xp_cmdshell @Command
Make sure that 'C:\Progra~1\winzip\wzzip.exe "H:\SQLBKUP\test.zip" "H:\SQLBKUP\test.txt"' is a single long statement in one line(no line change).
Command line tool that is being talked about can be downloaded from
http://www.winzip.com/downcl.htm
HTH
MJ