PCJ

Here's my problem: I have one computer on one floor, and the other on another floor, but at the exact same space. The direct distance between both would be 3-4 meters, but a cable would take 30 because we're not allowed to abuse the walls.
So I decided to set up a wireless network... until I realized that I don't have a clue as to how it works. So, here are my questions.
1. I'm currently on an adsl line, but my switch connections to another xDSL (but not nescessarily adsl). Will my network work with both?
2. Can I have the pc that the wireless router would be next to connected with a cable instead of wireless? That would save me money for a pci card.
3. I want to be able to use the internet without the restricions of a hardware firewall. The SP2 software firewall and zonealarm are good enough. Can I have an unrestricted connection and still not have anyone outside of my family f*** with my network? I heard that there was a way to set it up where you only allowed certain PCs to connect, is that true?
4. I'm an idiot when it comes to networks. I want this to be as easy as possible, everything else is secondary. Which company has the best tech support (ie guys that actually listen to you)? I was considering getting all netgear, just for avoiding any conflicts, and because their products are always pretty good.
5. I don't have any highlevel data to secure, but I really don't want anyone leeching away my bandwith from the outside. I need good security.

I guess that's about it. Any help welcomed.