Use the Module Management Tool to install the LinkItemToSpaceAction Amp. Information about how to do this can be found at: Module Management Tool Guide
The Module Management Tool can be downloaded here.
If the LinkItemToSpaceAction is installed you can do the following steps to link an item or a space to another space:
Click the 'Details' button of the space or the item you want to create a link of.
In the details view click the 'Run Action' link.
Now you can choose the 'Link item to folder' action
Click 'Set values and add' and choose a destination for the link.
Click finish and the link is created in the destination folder.