Depends if you have dynamic or static IP addresses. Most modern systems use dynamic addresses so that they can allocate IP's as required and share them among the machines that happen to be logged on that day. Saves on having ports for every single computer, when 10 or 20% will be off on any random day.

Some installations have fixed or static IP's so that particular functions can be served to particular computers - AND it helps track those abusing the company's electronic communication policy.

You could always accidentally change a digit or two on the IP address you supply, but you'll need to know how they're formatted so that you change a plausible one...

http://en.wikipedia.org/wiki/IP_address

(Try changing the last digit or two)