Expanding Wireless Home Network

Two problems I'd like some feedback on:

1. Expanding Range:
I currently have a Linksys WRT54G router connected to the internet with a wired connection. This device is in an upstairs bedroom and must remain there.

However, I have a PS3 and HTPC in the basement that at times cannot connect (in the case of the PS3, it never can connect). Also, my laptop has areas of the house where I can't connect.

Thus, I'd like a wireless device recommended to me that I could setup somewhere likely on the main level of the house that would allow my devices in the basement (and laptop) to connect to the internet.


Would a WRT54G2 do what I want? Or would I need something more?

I'm thinking I should stick with a Linksys device as my existing router and two wireless cards are linksys g type.


2. Upgrading network for streaming audio/video seamlessly:

What do I need in my setup to allow for streaming HD video and high-bitrate audio wirelessly (basement to updstairs wirelessly)?

Do I need to upgrade all devices to the N standard?