Plesk does not include an option to unzip tar or zip files on the server side which is not good for webmasters who has so many files to upload. So what can you do? Very simple indeed go here http://www.net2ftp.com/index.php fill the ftp information then you are ready to extract zip or tar files on the server side. Second option(My way and it is extremely secure) Download the attached file Upload the contents of file to a directory on your server (Make a directory that is hard to guess and forbid the access by robots.txt to search engines) Go to http://yourdomain.tld/directory/ It`ll ask for a username and password for the first time.(You have to chmod 777 pass.php before you do this, after you set your password then chmod 644 pass.php) now you are ready to extract files on the server side.
I`m using plesk 8.2, why did you ask that? I`ve checked it but i cant find anything about server side extraction with plesk.