Well I'm from Portland, what would you like to know?
Here's a few sites to look at:
http://www.trimet.org (there's actually a lot of information here)
http://www.metro-region.org (Metro is the MPO and is in charge of much of the area's transportation planning)
http://www.trainweb.org/aorta/max.htm (from the Association of Oregon Rail and Transit Advocates, also known as OreARP)
http://www.sts.siemens.com/DS/SD660%20Portland%20DS.pdf (fact sheet from Siemens, builder of the Type II, III and IV LRTs)
http://www.portlandtransport.org (local transportation discussion blog/forum)
Essentially the MAX system comprises of four routes in operation and a fifth route under construction:
Blue Line - Hillsboro-Beaverton-Portland-Gresham (the Portland-Gresham segment is the original line built in 1986; west of Portland opened in 1997)
Red Line - Gateway TC to Portland International Airport (trains continue from Gateway TC west to downtown Portland and Beaverton TC)
Yellow Line - Rose Quarter TC to Expo Center (trains continue from Rose Quarter to downtown Portland using the 11th Avenue turnaround, the old western terminus of the line)
Green Line (under construction) - Gateway TC to Clackamas Town Center and Rose Quarter TC to Portland State University via 5th/6th Avenue Transit Mall. (Trains will use the Blue/Red line route between Gateway TC and Rose Quarter, crossing the Steel Bridge and then enter a new alignment serving Union Station, crossing over the Red/Blue Line at the Pioneer Courthouse at grade.)
A MAX line to Milwaukie is being planned right now.