have you check out this site??
<a href="http://www.free-codecs.com/download/K_Lite_Codec_Pack.htm" target="_blank"><a href="http://www.free-codecs.com/download/K_Lite_Codec_Pack.htm" target="_blank"><a href="http://www.free-codecs.com/download/K_Lite_Codec_Pack.htm" target="_blank"><a...
<div class='quotetop'>QUOTE </div>
before doing anything check for spywares/adware and viruses. do diskclean up then defrag.
that should minimize some lagy problems.