I have not more experience with using drop-box but as per my experience you can use Dropbox with Outlook. It's actually quite simple. You will want to take the following steps:

1. If you don't know where the Outlook.pst file is located, go to Tools > Account Settings > Data Files tab, and note the location for the "Personal Folders" file. Close Outlook if it's open.
2. Copy the file Outlook.pst from its current location to your "My Dropbox" folder.
3. Once you've copied the file to your Dropbox folder, open Outlook, go back into the Data Files settings, and add the file you just copied by clicking the Add... button right under the Data Files tab.
4. Once that's done, go ahead and select that file and click the Set as Default button up top, and you're done. Optionally, remove the file that was originally the default from the list of files.