I need to change the time on my VirtualBox winxp machine (I have an ubuntu host), but it automatically syncronizes with the host. I need different times on the machines because I'm developing something which won't rely on the client's time.
Right click on the clock, choose "Adjust Date/Time." The rightmost tab should control syncing the clock with the Internet. Just turn that off, and you can set any time in WinXP and have it stick.