An iPad is designed to only be synced to one computer at a time, the message means that it's been synced to another computer's iTunes, and that syncing it to your new computer will replace the current contents of your iPad with the contents of that new computer's iTunes library.
You can copy iTunes purchases from a device via File > Devices > Transfer Purchases (if your laptop is a PC and the drop-down menus an't showing then control-B should get them to show).
There are some programs listed half-way down this page which can copy non-iTunes purchases (e.g. music copied from CDs) from a device : Recover your iTunes library from your iPod or iOS device
Or you can copy your library from your old computer : How to move your iTunes library to a new computer - Apple Support
You can also home sharing to copy content between computers (if they are on the same wifi network), or add it from your backup of your library/downloads via File > Add To Library
There are some steps on this page for syncing a device to a new computer (the page was written specifically for iPhones, but it applies to iPads as well) : Syncing to a "New" Computer or replacing a "crashed" Hard Drive
Some of the steps on that page have changed slightly (it was written for a previous version of iTunes) :
5, is now File > Devices > Transfer Purchases
6, 'Reset Warnings' at the bottom of the phone's Summary tab in iTunes
7, File > Devices > Back Up
8, File > Devices > Restore from Backup (or Restore Backup button on the Summary tab)