VNC with a router

[saint]

i have been using VNC for a year or two, it has been great.  so far i was
using it from a static IP address, now i have a static IP address, but i am
using a router.  I have a cable modem service, and i use a router to hook up
multiple computers.  my roomates and i can VNC between our computers, but we
can not VNC from out side the router.  the router gives us different IP
addresses....is there any way around this.  is there a way that i can set the
router up to so that i can use VNC.  any instructions or insight would be
greatly appreciated.
~thanx
    steve