dual os?
you mean dual boot I believe...dual os I guess would be something like vmware or colinux
http://www.colinux.org/
dual boot is just setting up a boot loader and keeping windows and linux on different partitions
it's relatively easy with a fairly modern distro.
Most neophytes get drawn to either mandy, fedora, or Suse first, also many other newb friendly distros exist.
I cannot attest for any of them myself because I never have used suse or fedora (stay away from redhat 8
) and haven't touched mandy since 9.0
I do suggest is that you download the
knoppix livecd and try it out first, (runs from cd and does not touch the hd unless you ask it too)
goodluck and remember these two very important pieces of advice...
google is your best friend
Read the effing manual