If all of this makes your head-spin, tell us your (a)
router make/model,
(b) desktop OS, and anything else you might now about your config and we should be able to walk you through it step-by-step.
Something else that might be useful is your current IP (to see if this is even possible). This isn't necessarily the IP address reported from
http://whatismyipaddress.com/, but rather what your router tells you. If you aren't sure how to get this, tell us (a) and we can help you out with that one. Also, are you running any third-party firewall software (ZoneAlarm, Norton, etc)?