Do you still have your old computer so that you can copy your iTunes library over from it ? If you do then there are a nubmer of various methods that you could use to copy it over : http://support.apple.com/kb/HT4527
You may also find this article on syncing to a new computer useful : https://discussions.apple.com/docs/DOC-3141
And there is also this article on recovering content from a device : https://discussions.apple.com/docs/DOC-3991
Of course it wants to erase the device if there is nothing in the iTunes library. Your iTunes content doesn't download to a new computer from iTunes.
You can transfer the iTunes library from the old computer to the new one if you still have the old computer. There are a number of article here that explain how to do it.
If you no longer have the old computer, you need to transfer the iPad contents into the new laptop before you can sync with it. Read this user tip. It talks about using an iPhone but it works the same way with an iPad.