Right click on your Ethereum Wallet icon and select properties
In target box add --mode mist to the end of the 'target'
Start Mist and wait until it is in sync. Then select 'browse' button
Select the address bar and enter in https://vote.daohub.org/
Note: You go to a test version by using http://vote.daohub.org/#T159fe90ac850c895e4fd144e705923cfa042d974 instead
Click the plus symbol to add this page as a 'DAPP'
Select the account you want to use for voting
Click on "Yes" or "No", to indicate your vote
Enter the wallet password. You would have created this when you created the wallet
Congratulations, you voted. Now click "Got It" and continue to select other proposals to vote on, or close your mist browser.
Step by step, coming soon, but in short you need to open mist with the Ethereum Wallet 0.7.4 from the command line with --mode mist