Open DM, click synchronize, click configure synchronization in the left hand side of the window, click the button that says synchronization, a Wizard will appear asking you what you want to sync (contacts, calendar, etc.). Check the box for Yahoo, follow the prompts, and click finish when it is done. It is exactly the same as the steps for Outlook, you just need to check Yahoo instead of Outlook.
I don't use Outlook either, but I had no issues with syncing to Yahoo. I sync my contacts and calendar. I do 2-way sync so if I change something in Yahoo it gets changed on my BlackBerry and vice-versa.
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