Setup shares and printer on a network

Hi Guys,
I need some help please, Ive got 4 computers hooked up to a router, 3 of the machines are Windows Vista Home and 1 is XP.
so its a small network so to speak.

Heres what i need help with, would be grateful if i could get some step by step instructions on this
as i haven't configured anything like this before.

Machine A Windows Vista Home
Machine B Windows Vista Home
Machine C Windows Vista Home - printer hooked up to with by USB cable
Machine D Windows XP


1.I need to create a shared directory on A and B and set-up so that they can see/access each others share,
2.also need to create shared directory's on C and D and set-up so that they can see/access each others share,
3.Configure so that A and B can also see/access shares on C and D but C and D cannot access the shares on A and B.
4.Machine C has a printer hooked up to it via USB cable, how can I share this printer out so that all machines can access it, the printer is a HP Color LaserJet 2820 All-in-One

how do i got about doing the above?

printer info
http://www.shopping.hp.com/webapp/shopping/product_detail.do?storeName=storefronts&landing=printer&category=LaserJet&orderflow=1&a1=Color+printing&v1=Color&product_code=Q3948A%23ABA&catLevel=2

any help would be great, all the machines can see each other i tested this by pinging....

Thanks
Jay Eire