P0440 Code... but not the gas cap

I have a 2001 Alero 4-cylinder. Recently I started getting the P0440 code, so I bought a new gas cap. Unfortunately the trouble code came back. Maybe it's a coincidence, but it seems to only come on when the gas tank is less than 1/3 full. Anyway, I read the possible solutions on the OBD codes site:

http://www.obd-codes.com/p0440

and on this thread:

http://www.automotiveforums.com/vbulletin/t622461.html

Now that I know it isn't the gas cap which of the next solutions are easiest for me to check before bringing the car in? Does anyone have pictures of where the purge solenoid,sensor, and canister are located? If this was a major leak wouldn't the code come back on right away (or at least fairly quickly). It only comes back after a week or so of driving. Thanks.