Driving a car:
You can figure it out on your own.
Buses that you can take:
#75 St. Johns, stops at gathering point.
#40 St. Johns, stops at the Willamette Blvd end of the park. From there, walk north through the park 'til you find the rally.
#1 Greeley and #4 Fessenden also run in the vicinity (several blocks north of the park.)
Wherever you're coming from, if you log onto www.trimet.org and click on their "trip planner," you can enter your address and the place you want to go (N. Lombard & N. Woolsey), the time you want to get there, and it will give you routes, transfers and times. For those taking the #1 or #4, you can go to www.mapquest.com to find a map of the area, which can then help you find your way from the bus stop to Columbia Park.
Please note that the Portland Police aren't very bright, and are notorious for causing severe traffic disruptions. Anyone who's participated in a Critical Mass ride knows that the cops are ten times worse about blocking off traffic than the bicyclists themselves. Therefore, bus travel may experience significant delays or potential re-routing. Hopefully (for the sake of N. Portland neighborhood residents) public transit will be kept running smoothly.
For many people this will be a loooooong bike ride. However, it's the most environmentally-friendly and dependable method. If you're riding a bike, you _will_ be able to make it to the site, which can't be completely guaranteed for car and bus travelers.
To make it more fun for bicycle riders, and to encourage solidarity, it's recommended that people meet to ride up in groups to the event. Hopefully people will suggest more initial meeting points or join up with others along the way. From talking to various people, locations that have been suggested were to meet at Ladd's Circle in the heart of Ladd's Addition at 9:30 am, the Citybikes Annex at SE 20th and Ankeny (no time as yet), and the intersection of NE 15th and Broadway (no time as yet).
The best route for bicyclists to take would probably be to head north on Interstate Avenue, take a left on N Portland Blvd, and then a right on N Willamette Blvd. This will safely take you to the protest site at Columbia Park, with bike lanes along this route. N Lombard is another option, but traffic is heavier and there are no bike lanes.
Safe journeys, and hope to see lots of you up there!