Well you should have all the info in the box from Palit/Amazon required to activate any warranty you have.
Often there's a wee card or something you need to fill in. But sometimes you don't need to activate it and it simply works from date of purchase/receipt
i was thinking maybe its just activated as soon as i buy it from amazon. i have returned other products without needing to have applied for warranty on them to amazon.
all that came with the product was a little manual and the software cd/dvd.
That very well may be the case, remember you would potentially be returning it direct to Palit and not to Amazon though.
Although that might be a bit confusing, according to Palit's website you need to request the RMA via your vendor (so in your case, Amazon) http://www.palit.biz/palit/rma.php?lang=en
Doesn't mention anything about returning any warranty cards etc. though so you're probably ok and it'll have been warranted from the time you purchased it.