Hi - you are automatically covered for Warranty (usually 1 year or 3 years depending on the model you have bought) - you can check your warranty entitlement here - http://www.fujitsu-siemens.co.uk/suppor ... y_ent.html
Notebooks do not normally have to be registered for warranty unless you have also purchased the extra "extended warranty" (either to extend the period from 1 to 3 years or to get extra level of service). If you have purchased the additional extended warranty then you will have to register this at the website http://www.fujitsu-siemens.co.uk/suppor ... index.html
(if you are UK).
You should have received an activation key with your extended warranty - if you did not, then you should contact your reseller.