np on the typo, i just wanted to be sure

The cable "tip" was before XP was released, so where/if the same option is in XP, i'm afraid i dont personally know. As for the XP firewall not being turned on and whether it would effect you or not, i would check elsewhere first.
"behind an SMC switch".... do you mean you are using an SMC router? Have you done the forwarding ports and put those in mIRC's options as in the post i referred you to? There was a recent thread from a user having probs with SMC, one thing i suggested was to try something other than server port 6667... when he tried 6668, it worked fine (to see that thread put SMC in the search feature, connection issues, i think it wasnt much more than a week ago)