I checked Seagate site and they provide 3 years warranty only for retail customers. I just ordered a replacement HDD and (in case it fails) it can be exchanged in the next 3 years.
Dell's warranty for my Vostro 1440 has expired 12/15/2012 and my ST320LT020 HDD is failing according to Dell's diagnostic utility. According to [URL] this drive has "3-year limited warranty". How can I access this Seagate warranty? 
Seagate warranty for failing HDD after Dell's warranty has expired