Computer help needed !

[Trueoo7]

I think I work on my Cobra too much because when it comes to computers I'm not at all fluent so I'm looking for some help. I need to set up my house for wireless internet. I would like to run one.... maybe two desktop computers and a laptop aside from the main desktop computer that now has a cable modem (Broadband) hooked up to it. The house is three floors, main computer is on the middle floor. There will be one upstairs and one downstairs that I would like to run wireless as well as a laptop floating around from time to time.

What do I need to get? If you have names and model numbers that would be great as I've tried to read through some different ones but don't know what to look for or, whats needed. I know I need a wireless router but whats needed on the other end for the computers to pick it up. They are about five years old and are running Windows XP. One has two USB ports and the other doesn't, although I've seen adapters that plug in to the other type of plugs that turn them into USB ports. Cost is also a consideration so if you have a ballpark figure that would help as well.

Technology changes sooo quickly that its hard to keep up.
Thanks

PS I have a 2.4 GHZ cordless phone, I've heard they can interfere with routers.