after changing to domain , i noticed that the pc is getting too slow ,so i watched what is the reason, and i found that lsass.exe (local security authinitice services) is taking about %50 of the cpu use ,i looked in ms help website, but they have nothing,does anyone have an idea why.

I saw this happen on a W2K machine in the past, and turned out to be a security bug with the OS. If you are an official beta tester, I would submit a bug report on this.