No it doesn't Look around the Forums
Unless it's done by a certified apple technician, replacing the HDD of the MBP DOES void the warranty on the MBP. technically it's not a user-replaceable part. but i guess it'll be considered void if they notice that the drive is different from the specs of your purchase. there's supposedly a sticker/seal but if you're really careful i guess they won't notice. replacing RAM won't void the MBP warranty.
on the MB however, replacing both HDD and RAM won't void its warranty.
4. You can get a MacBook, 4 GB memory, replacement 320GB drive, spare external drive from the internal one, and if you use it say half the time on your desk, you can buy a 24 inch monitor, mouse, 500 GB extra drive, and a backup drive for Time Machine, and still pay less than for a basic MacBook Pro.