I don't really know if this answers your question, but... I think you may be asking "How do I do this?"
Anyway, I'm on Windows 7, and I know it's very similar to Vista, from way back. Type in the search box "Network and sharing center"... Click on that.
Now that you are in Network and Sharing Center, look at the left hand column thing at the top left. You will see "Change Adapter Settings"... Go to that.
Now, you should already have your Ethernet cable attached to this second computer. This connection should show up in this Adapter Settings menu.
Now if you already have LAN on your first source computer, you will select that connection in this menu. Now, you will also select the Ethernet cable that is going to your second machine. If they are not right next to each other, you can do...
Ctrl + (click) and you will be able to select multiple items in the menu. Now, right click and choose "Bridge Connection"
Now on your second machine, you should have a connection pop up in the little wireless menu on the bottom right in Windows (whatever version you are using). If it asks you to sign in, as you may have a password set on your network, then do so as normal, I guess.
Now I've done this with my PS3 way back, as the connection from the system was not strong enough to stay connected, but my laptop at that distance, was able to, so I eventually arrived at this method.
I really hope this is what you're asking for, as I don't fully understand your post. But even if it's not and someone finds this helpful, I'll still be satisfied. Good luck.
P.S., I'm a noob. Isn't a "crossover cable" just another way of saying "Ethernet cable"? Unless they aren't the same thing, and I've just seem them used interchangeably, which I guess would just be a case of getting bad information.