Vista Tutorial - Need help connecting two computers please

I am trying to connect two computers with a crossover cable.

Computer "A" has two onboard ports and one is used for the Internet. It
is running Vista Ultimate.

Computer "B" has two available ports, one onboard and one Ethernet card.
It is running XP Pro.

I have connected the two with a crossover cable but can't get it to
work. I'm not sure what else I have to do. I've tried browsing the web
but what I've tried didn't work either.

When I unplug the connection from "A" a network connection unplugged
message pops up on computer "B". As well, computer "A" shows the
network in the network folder but it has no connection. It shows the
Limited Or No Connectivity message.

Can someone tell me what I need to do on each computer please? Thank you!