please help me!

ok, from the start i wanna say that i'm from italy and my english isn't very
good. So, my problem is very big and kinda stupid...i bought a windows xp
home edition but from a big stupid reason i throw all the envelope and other
things that was with the cd, i know...not a very good ideea but what can i do
know....i mean how can i find out my serial number because its not on the
cd...isn't there any chance for me to find out the serila number for this cd?
i don't know...like writing at the microsoft site any other code that is
printed on the cd? pls HELP! i spent like 100 euro on this stupid cd and i
can't do anything with him now.