Try this..
private string[] ExpandZipFile(string ZipFile, string DestFolder)
{
Shell h = new Shell();
Folder sf = h.NameSpace(ZipFile);
Folder df = h.NameSpace(DestFolder);
string[] files = new string[sf.Items().Count];
int i = 0;
foreach (FolderItem f in sf.Items())
{
df.CopyHere(f, 0);
files[i++] = f.Name;
}
return files;
}