I think the easiest way to tell if any vehicle is capable of 4 wheel drive is to just look for the shaft that goes to the rear axel and the two trans axles for the front..ie take a look under the vehicle. As for your question about the two buttons on the shift lever, one is definitely the release for shifting into a gear and the other looks to be O/D not D/D (take another look).
O/D is for over drive. Fancy term to let you know that your van is using all 4 gears (or three...I forget with the van)...well all that it has. IF it is off, there will be a red light on the dash say something like " O/D OFF" that would mean you are in 3rd gear if you are at the van's cruising speed.
O/D off for hill accent/descent or for extra passing power. You've basically down shifted.
O/D on for fuel efficiency.
Edit:
I add in the other thread you made that you should try
www.Amazon.com for those repair manuals. I've found that amazon often has book stores clients who will ship overseas.