I take it that you already have the network on place and just want to know how to share your hard disk. Here is a fairly simple way.
On your mac, open terminal.
write 'cd /etc' with out the ''. press enter
then write 'emacs smb.conf' press enter
you will see a bunch of stuff...scroll down by the arrow key. you will see
[global]
some stuff
[homes]
some stuff
After homes and its stuff paste the following
#--------------------------------------------------------------------------
# hard disk
#--------------------------------------------------------------------------
[Hard disk]
comment = "Hard disk"
path = /Volumes/name of your hard disk
browseable = yes
guest ok = no
read only = yes
create mask = 644
directory mask = 755
you are done,Now save the changes - hold ctrl down, press x, release x, press s.
NOw exit - hold ctrl down, press x, release x,press c.
SO what you did above, was to make your drive as share, just as the default public folder.NOw just make another account, and when you log on to this account from windows or other systems, you would have read only access to your drive
hope it helps
cheers