cant watch movies

ok here it iz then : i cant watch the movies and tutorials in main menu.
always same prob ,"click here to download plugin" 2sec later after the click..
"firefox is now checking for availeble plugins... >no suitable plugins were found" i tryd a windows codec pack but that wasnt working either,so anyone can help me out here pls ?
(i use an ordinary pc Pentium 4,Windows XP Professional)