my wife, myself and my dad (83 yrs old),who is in fairly good shape, are staying at the Wyndham on "m street". how far is the walk to the WW 2monument , the vietnam wall and posssibly some museums such as the "spy museum".many thanks for your help

The hotel is at 14th Street, up behind the White House in an area with other hotels and several embassies.

Since you'll need a map when you're touring, why not get one now, and be your own judge, since only you can really asses your group's stamina. The area is pretty flat for walking.

DC taxis are cheap. They don't have meters, or charge by distance, the whole system is zoned and everyplace you've mentioned is all in the central zone so you'd only pay about $5 for your group of 3 to get from your hotel to the nearest monument (Vietnam) and you could walk the rest form there. The Spy Museum is closer to your hotel.

If I was to take a cab to the ww2 memorial,how close would the cab bring me? Trying to decide whether to bring a wheelchair for dad.He`s never used one before and I don`t want to bring one unless I have to.

A cab will drop you off at the curb right next to the WW2 memorial.
Check out the official website for more information:
http://www.nps.gov/nwwm/

Your hotel is centrally located in DC but not very close to any major attraction or Metro station. Plan to use taxis; anywhere you are likely to go will be within the central fare zone.

Yes, the cab will drop you right in front of the WW2 Memorial like kayd said above, but it will also be easy to catch a cab there when you are done as the cabbies continually cruise this section of curb.

All the replies are wise. Use cabs.