Hey Hey,

It all depends on where you are trying to find the IP. You could tail your apache logs and you'd see the IP of everyone who connects to your webserver, the same goes for any other server you are running. You could ping the hostname like Vigge said or you could use nslookup or dig if you have the hostname. If you are on an IM like MSN or Yahoo then the advice that bludgeon posted is your best bet. If you are on the same LAN ping the computer name and you'll get the IP back.

Of course the easiest way is to just ask them, but there are several methods you could use.

Peace,
HT