If you want to go single speed and not fixed, it sounds like you will need to remove your shifters and derailleurs; shorten your chain; replace your multi-speed freewheel with a single speed freewheel; and re-space and re-dish your rear wheel. You might also want to take off one of your chainrings. You don't need to buy a new wheel or crankset.
If you want to go fixed, you can do the above and run a "suicide hub" or you can be a safety ranger and buy a new rear wheel that is designed for riding fixed. I suggest you read Sheldonbrown.com and look at the bob's garage videos on Fixedgeargallery.com
Your 710 shoud make a great fixed gear. Enjoy.