You question is extremely vague. You're getting vague answers in return. Plus itz tuf ot reed stuf tahts speld like ths.
Please be more specific about your setup -- what model of router? What kind of modem? Does "mini airport thingy" mean AirPort Express? We understand that one end of the ethernet cable you've got plugged into your computer -- where is the other end connected specifically? If your modem on a WAN or a LAN port?