I don't know much about this, but as far as I've understood the whole 64-bit thing, the only difference is that you can have more RAM. But the current 64-bit laptops are not able to use that much RAM anyway, so what's the benefit of it? Of course the C2D processors are great in so many other ways, but it seems to me the whole 64-bit thing is blown a bit out of proportion. Please enlighten me, as it's probably just me who missed out on whatever the big thing about 64-bit is (apart from more RAM).
(sorry for being off topic)
This should help:
http://en.wikipedia.org/wiki/64-bit
And since that article is waaay too technical these appear to explain it in simpler terms:
http://www.pcworld.com/article/id,111508-page,1/article.html
http://arstechnica.com/cpu/03q1/x86-64/x86-64-1.html