It's a bit clunky, but:
1. Use find and replace to replace every space with a paragraph break. (Type a space in the Find box and ^p in the Replace box, then Replace All.)
This will give you a very long document with every word on a separate line.
2. Use find and replace to strip out all punctuation.
3. Select the whole document and Sort alphabetically. (In older versions of Word, Sort was in the Table menu. In newer versions you'll have to hunt for it.) This will give you all the words in alphabetical order.
4. In newer versions of Word, there is a Word Count toolbar. If you open this, it gives you running stats on word counts. Select groups of words to get the stats. Otherwise, a workaround would be to apply auto-numbering to a group of words to see how many there are.
That's all I can think of. Good luck!