It says that the wgames app installs .ipk files. The Preenv FAQ mentions 7zip if you're installing games 'manually' - ie, if you're not installing using something like wgames. wgames *might* need 7zip or similar, but it should have installed any dependencies when you installed it. (I don't know - I don't use wgames). Have you tried installing a .ipk game using wgames yet?