Vista and XP Network password problem

I have Vista HP on my laptop and have a network of three PCs two of which
have XP Pro and one has Vista H. My Vista machine can network and share as
normal, like I did quite easily with XP Pro, however Vista & XP have issues.

My Vista machines can look and work with my XP machines without limitations,
however my XP machines can't do the same. I keep getting asked for a
password. I would just like to share a few drives and folders like I have
always done.

Can anyone offer assistance as this is now getting anoying.

Hope you have all had a happy Christmas and I trust you'll have a happy New
Year.
All the best for 2008.
Lloyd