I've never used the linksys that Ravin mentioned, but most everyone here recommends it. I really like the netgear equipment I use, but some people don't like netgear. I have never had any issues with my netgear or linksys equipment.
Nope, just need the 1 router. It has a 4 port switch built in to it, so you can hook up 4 machines to your router. If you need more connections, you can buy a multiport switch.
you need a wireless router.. and then wireless cards (adapters) for each computer... that's all.. you can get a pci card, a usb, adapter, or cardbus for a laptop.. and a lot of laptops have wirelss built in..
Do you want both PCs on wireless, or just 1?
Anyway, get the router that was recommended above. Then, you have to decide if you want a wireless adapter that plugs into the USB port, or that you plug into a PCI slot. If you aren't comfortable opening your PCs, go with something like this: http://www.newegg.com/app/ViewProductDesc.asp?description=33-124-126&depa=5
Otherwise, different people have differing opinions about PCI vs. USB desktop PC wireless adapters.