What tcsoccerman said. It is especially important, while playing Continuum, to close other programs which may access the Internet. This includes (but is not limited to!) instant messaging/chatting programs (such as AIM, MSN Messenger, Yahoo! Messenger, Google Talk, Skype, etc.), Internet browser windows, Internet chatrooms, filesharing programs, stuff like SupportSmith, and the like. Heck, even make sure any other programs (especially antivirus programs/firewalls) you may have (this includes Windows Update) aren't automatically checking for, or downloading, updates while you are in Continuum.
In short, make sure you aren't downloading or uploading any files over the Internet while you are playing Continuum.
If other people in your house (i.e., using the same Internet connection) are online while you are playing Continuum, they may be causing your lag. Either ask them to minimize their Internet usage when you are playing Continuum, or try to only play Continuum when they are away from their computers.
If all else fails, try what blue monday suggested and play during the 'off-hours', i.e. late at night or early in the morning. Especially try avoiding the 'peak' hours, i.e. late afternoon/early evening.