Many component and hardware companies these days do not require or even allow you to register your product. Simply keep a record of your purchase information, and it would be a good idea to scan a copy of your purchase receipt or shipping invoice if you don't have another digital record of it such as an email showing the purchase from the retailer, like Amazon, because paper copy receipts and invoices tend to fade with time.
So long as you have that documentation in some form, they will honor the warranty if something goes wrong and you need to RMA the product. I don't see any place on their website to register a product at all.
If you DO have a problem, you can use this form to contact them about it. You might actually be able to use it to contact them regarding product registration as well.
http://www.inno3d.com/support_form.php