Watching films,videos on my pc

Question

hi mewms.when i try and watch films on my pc the screen flickers and freezes i have the klite codec pack and i also have vlc media player. but vlc only plays sound but no video. i was running a much lower spec computer with only vga graphics and using the same codec pack and player and had no problems at all.im using a 1.1 celeron (dont laug i had a better computer but i had to sell it to get some cash) with 512mb ram (but it is only showing as 256mb and my computer can handle 512mb)running xp home sp232mb graphics cardhave you any ideas what this could be maybe the card id no good..?much apreciated thanks james