Lynne, I was poking around the Cycle Oregon website (that's on my list of rides I'd like to do someday!!) and came across this link to a Portland-based training ride series that was offered this past year:
http://www.trilevelfitness.com/performance/
Perhaps they'll be offering something similar for 2005?

Also, I recall there were some training ride series in the PNW meant for preparation for the STP (Seattle-to-Portland), which is a 200-mile ride; participants do that ride in either 1 or 2 days. Anyhow, you might come across a training ride series for the STP in the Portland area - hunt around your local club websites, or maybe the website for the Seattle-based Cascade club might point you in the right direction.

I think joining in on training rides that are set up in preparation for a specific event (such as Cycle Oregon or STP) is a great way to gain fitness and gauge your progress, even if you're not participating in that particular ride. Training ride series are generally structured such that they are progressively longer/more strenous, so that if you complete the series you'll be prepared for that particular ride (in theory ) Also, they tend to divvy up participants by ability level so in general you'd be in a group that is roughly equivalent in terms of speed & endurance.

hth, - Jo.