There is currently no built-in import tool. This feature is on our customer wish list, but we do not yet have a release date for it.
You will have to either manually submit the warranty info or write a script to insert it into the database. An example script can be seen below. It updates the purchase date of computer "LAN-001" to January 1st, 2012.
UPDATE tblCompCustom
SET PurchaseDate = '01/01/2012'
FROM tblCompCustom INNER JOIN
tblComputers ON tblCompCustom.Computername = tblComputers.Computername
WHERE (tblComputers.Computer = 'LAN-001')
