cant get rid of cpu lag spike, HELP PLZ

i get a 100% cpu usage spike about evry 10 sec. it makes other progs/games lag....very annoying. it seemed 2 start after i got windows media player update. ive tried a couple things from other forums, like uninstall windows indexing and a spybot, but nada. still there. my norton av also is auto closing after i open within 5-10 sec. i run xp on a p4 2.66, 512ddr, radeon 64mb vga. any suggestions appreciated. thnx

oh i forgot, during the spike, task manager sez a lsas.sys is taking up around 60% of the cpu....if this helps