When you right click on a file or folder, you can move it to the Dropbox folder
If you already have a shared folder in the Dropbox folder, you can also add them to the Send To menu along with the same method. As in the example, we're adding a shared Dropbox folder.
Add Dropbox to Send To in XP operating system
In Windows XP, go to Control Panel > Folder Options > Show hidden files and folders.
Go to C: Documents and Settings [User Name] SendTo (User Name is the name of your computer) and create a shortcut to the Dropbox folder.
Now you have Dropbox folder added to the Send To section in Context Menu.
If you use Send To in the Context menu, it's easier to add files and folders to the Dropbox folder.
( Source : Howtogeek)