<p>How do I set up a network between the Host and the guest OS in Windows vista?</p>

I don't run vista, but virtualbox should do most of the setup for you - all you need to do is assign an IP address, subnet mask, and (optionally) a default gateway to your guest OS, and it should just work.
Don't bother with any of the advanced network settings in the options for the VM - they're useful in some situations, but I've never had to use them, and I've been using virtualbox for some years now.
If you post the specific problem you're having perhaps I can help more. But your question is rather vague...