the only thing wrong I saw with your screenshot is it forwards a range ie x to z
so if its just say port 80 it should be 80 to 80
Also double check your firewall rules.
https:// ; http:// ; https://******:80 all possibly ways you could of easily configured the web gui. if your getting dhcp... its there :p
edit:
also I know firefox is a $%$^ when it doesnt know the encryption key (or w/eprotcol it is I dont remember) and it almost looks like 404 and you have...
Your wins resolution most likely most resolve on the macs. Hince why everyone is asking if your connecting via IP. Most likely this sounds like your solution.
I apologize for not reading your whole post but I would recommend turning off windows firewall. Especially if your having issues with whatever connection your on. Happy holiday hunting for your solution
Rayman. Linksys repeaters work with linksys routers for some reason. Think they know what is what based off a mac. I have never gotten a linksys to repeat a signal from another ap (of non linksys type). There might be some hacks for this but I doubt it. I think client mode has the same...