like swerdna, i’m a bit confused by the way you ask the question…
if your questions is:
Q1: Can i install openSUSE on my Windows machine and then, when
booting can i choose either Windows or Linux to run?
A1: yes (it is called “dual booting”)
Q2: Then, when booted to Linux can i access (read, write, use, see,
listen to, change) files on the Windows NTFS?
Q3: If i boot to Linux and find thing on the net, can save them to
Windows NTFS and use/see it in either Windows or Linux?
Q4: If i find/create stuff in Linux and save them to my Linux /home
file system can i then read, write, see, use, listen to, etc those
things while i am booted into Windows?
A4: No, Window can not ‘see’ or access Linux file systems. (Why?
because Redmond doesn’t want you to use Linux, ever!)
Q5: But i saw on my friends machine a directory on his D: drive that
was like D:/Ubuntu, what was that?
A5: I have no idea but i can assure you that it was not a dual
bootable Ubuntu system! Well, maybe it was where s/he puts things
(like music) to be used on either machine…i do not know…
Q6: Can i run both Windows and Linux at the same time?
A6: Yes, launch Linux and start a VM, and then run Windows inside that
VM (or the other way, run Linux in a VM hosted by Windows–but, that
is kinda dumb, i think)…
have a read here: http://en.opensuse.org/How_to_migrate_from_Windows
thank you for your interest…