Assume you're referring to the Boeing 747/767/777 plant tour. It's in Everett, about 30-45 minutes drive north of Seattle. Info about the tour can be found at
http://www.boeing.com/companyoffices/aboutus/tours. I've never taken the tour myself--it's sort of like the Space Needle, which I haven't visited in 20 years--but I've heard it's quite good.
The Museum of Flight is in Seattle, about 10 minutes south of downtown at the southewest corner of Boeing Field. That one I do visit often--Concorde, all of the Boeing commercial jets, lots of warbirds and classic commercial craft as well. See
www.museumofflight.org for a guide and calendar of any special events.
You can drive Portland-Seattle in about three hours, but the trip up the I-5 freeway is a bit on the boring side, especially if it's raining. A quick hop on the Horizon shuttle gives you a better look at the mountains (again dependent on weather).