Do you know how to open an Existing PST?
In this case, you would be opening the Desktop PST that you shared across the network.
Most users only have one PST when they use Outlook in Internet Mail Only (IMO) form.
However, just like the Exchange setup, you can create and add personal Archives. In this case you have 2 options. Rename the Laptop PST to Outlook1 or Old.pst then open outlook. It will look for the Outlook.pst file and cant find it. It will ask for the correct location. This is where you select the shared outlook pst file location. It will then use the NEW pst as its outlook today main file and then Email will stay sync'd and happy with the Desktop. Now that you have achieved that, you just re-add by opening a PST and then select the renamed PST you used to use.
Old File: C:\Documents and Settings\MAIN\Local Settings\Application Data\Microsoft\Outlook\Outlook.ps > Outlook_Old.pst
New File: X:\outlook\outlook.pst < networked copy on the desktop
So that you dont try to confuse Outlook, you need to make sure the files are different names. See attached images. The Outlook folders is a list of both my main Outlook.pst and then the Attached Archive PST that is different location and information than the main. The image of Arhive Settings (misspelled the Filename

) Look at the file location and then compare with the file location on Outlook Folder Props image. This is what I am describing.